Introduction: Here I try to present some of the ideas could grasp (so far) about the causes of our mental inquietude and drives caused by it. Also, how it was interpreted in some epochs and by some thinkers .
There is a certain pleasure on execute things that is distinguished [here] in two categories. The first is the pleasure of archiving the end goal and the second as the pleasure in the activity itself. Both, or any activity we start or engage in is caused by a mental inquietude. Every mental inquietude, according to Antonio Damasio, is caused by somatic experiences; the reaction when we experience irritation, pleasure and everything in between. Reaction as striving for life balance. We react (emote), then create a mental picture (icon) of the experience which we associate to a meaning, from which we create feelings. Feeling, then, connect us back to mental picture, activating our memories (of experiences). We like to believe we are rational beings when in fact we are emotional beings. We learn, remember, think and execute things based on our mental pictures brought by emotion associate to them, even when we believe we are being pure rational, like in science.
We don't perceive the world and reality as it is but as we are. As the mental picture we have from our experiences are, and meanings associated to them. Our five senses are not meant to reveal us the world out there but to help us keep our life balance regulation (preserve and perpetuate life), in finding food when we are hunger, in find shade when we are tired, in identify danger to avoid and pleasure to chase. The evolution presented us with our mental capacity in order to quick, or better adapt in the short term, to our environment changes, increasing our chances of survival and life perpetuation. Nonetheless, we use our highly developed nervous system to attempt the understanding of reality. We can't experience all, or many, mental pictures at once but one by one and consequently the feelings associated to each of them - although we can experience them so quickly that we don't realize it. - It means that we experience our mental pictures in a linear way, which allow us to experience what we call as train of thoughts. As we are the tool we use to give meaning to reality, we fall in what Kant used to call as The professional thinker fallacy. We perceive time, reality, history and even science in a leaner and progressive way because it's how our mind - and our verbal communication - works; not because reality, time, history and science is linear and progressive. It doesn't mean science does not progress. It means that progress is subjective to our mind.
The will is a mental activity inquietude. Will is not merely the power or choosing or making decision - it's not a mere desire, strive or wanting. - It is rather a conflict between two drives: yes and no, as Hannah Arendt describes in her book The Life of The Mind. The will, before become a concept or mental organ known by philosophers, was interpreted as a duality in one person, as a hidden person inside a person. It's as to have two "I"s, the "I" who commands and the "I" who obey, which the second one perceive both "I"s as a whole willing desire obedience anticipation. The first one is the will. The will is the commanding thought, as described by Heidegger. We Will as overcoming this mental duality conflict.
Every mental activity ceases the sense experience and our senses experience cease our thinking, meaning that when we are thinking (our attention in our mental pictures - train thoughts) we are unaware of our senses perception. If something happens to grab our sense perception attention, we then become unaware of our thinking. In order to fulfill the will we act through our senses (act in the world) which once completed ceases the Will and put us at a mental fulfilling rest (no mental conflict/inquietude but just being), because we cease to want things once we get them.
The first kind of pleasure from execution that I mentioned at the beginning, that means reach to it's end, comes from the wish against the activity itself, which we do in order to overcome it, as an obstacle to or real goal. It's like the Aristotelian thought that says the goal of work is leisure, as the goal of war is peace. Once you execute the activity and reach it's goal you feel fulfilled and at rest, without mental conflict/inquietude (at least for a while).
The second kind of pleasure we have from executing things, is not in the activity end but in the activity experience itself. Duns Scotus, one of the most original and important philosophers from middle-ages, called it as love. The transformation of the Will in love. It's the activity that doesn't need to reach it's end in order to bring a restful mind. At the same time, because it never reaches it's end it never ceases the will. So the activity causes temporary pause in the Will expectation for an end, and such temporary pause, during the activity, causes us a constant fulfillment, the pleasure in the activity and not on it's end. Or in other words, the goal of the activity is not to get something once it's end (like leisure we expect get from the end of the work or peace we are after when we do war), but the goal is the activity itself.
Coming from a religious philosopher it explains that the divine love, or true love, is the fulfillment one have for a desired object not through possession (which would ends the desire) but through pure activities interaction/creation around, or related, to such desired object.
While for Nietzsche the will is a destructive power. The goal of the will is to become it's master, but once events happened the will have no power. You have no power in shape the past, or as in Nietzsche words: The Will cannot will backwards. For him, as well for Heidegger, it's the source of our duality (the will) conflict. What is left for the will frustration of not being the master of past events is to destroy it, by willing new events to pass in which the Will can be the master.
Ancient Greek philosophers didn't know the will, but they had a parable about the best athlete being the one who is not looking for glory or fame (the goal to archive at the end of the sport activity), but the one who finds the pleasure in the sport itself. Something similar we think today about artists, photographers or creators in general. The true or the best creator being the one not doing it for money or fame, but for the art sake. The activity not as a gateway to happiness but the happiness itself. Or as the Greek philosophers described, one as both actor in the stage of life and spectator of their own act. The individual duality working together and overcoming it's internal duality conflict (inquietude).
The Oriental thinkers (Daoism) had a similar allegory about life being a stage, where we act, but through our act we forget who we originally are, causing a conflict between our acting character and who we are inside. The conflict is solved when we realize our acting character and, from such realization, we become our own spectator of our own acting in life, enjoying the stage of life both as actor and spectator - enjoying the activity by finding fulfillment in it, doing it for it's on sake.
In a modernist philosophy this duality is interpreted as the social self and original self (this second called Being). The social self hides the internal Being. The Will is the spontaneous and intuitive pulse of our internal self (our Being) emerging during activities focused on the pleasure of the activity sake, as if enjoying our internal self emerging.
What the Ancient Greek Philosophers and Daoism have in common is the perception of life not as linear but as a cycle. In the west, the linear view of life and reality gained space specially because the way we associate our mental picture and meanings to our linear verbal writing system. The concept of a willing-Ego is only possible through such linear view of reality. During Middle-Ages and Renascence, both linear and cyclical philosophical perception of reality developed parallel to each other; as Hannah Arendt describes, Descartes and Leibniz in one side, Hobbes and Spinoza in the other side. Kant somewhere else. Our scientific path during modernism was influenced by the linear perspective which brought the concept of the Will. Such influence was mainly because of a linear religious doctrine imposed by the Catholic Church as political institution in Europe. As Antonio Damasio narrate in his book Looking For Spinoza, he [Spinoza] influenced our great thinkers and discoveries but in a hidden way, behind the linear perception that creates the contradiction betwen free will and causative effects of a linear event of life. The Inquisition banned any kind of Spinozist philosophy to be learned, used or mentioned for more than one hundred years, consequently (and accidentally) giving more highlight to Descartes philosophy.