I am a being with desires. Roughly, this means that I, as a sentient system, feel impelled to relieve an urge. So, I create a mental simulation of some thing, some state of affairs that differs from the current state of the world, that I expect (or hope) will alleviate that urge.
A simple example: Debra is hungry. Instinct and memory tell her that moving her body so as to bring comestibles to her mouth and chew (+ swallow, etc.) will make her less hungry. Thus, her object of desire is a state where she has eaten food, or where her stomach is full, or something to that effect.
The fundamental principle, as everyone already knows, is that actions modify our environment, and our bodies consequently reward us – with dopamine and the diminishment of urge – through modifying the environment in particular ways.
What happens, now, if I desire something impossible?
Let me sit and contemplate a bowl of fruit. My desire is for one of the fruit – a mango, perhaps – to be in my hand. I have, then, a clearly defined goal (a simulated aspect of the environment which will sate my want), and all that remains is to use the power of action to translate object of desire into actuality. Common sense says I should move myself within range of the bowl (if I'm not there already), extend an arm, and pick it up. However, my desire is slightly more complex than that: I want to achieve my goal without going through those steps. Part of my envisioned goal includes the condition that I collect the mango in the absence of gross physical movement.
There might be other options: maybe I have a friend (or servant) nearby who will interpret a very slight gesture on my part as a request for the mango. Or maybe there's a mechanical hand and conveyor belt set up that leads directly to my own biological hand, and it is activated through some minute action – moving my eyes or blinking in a particular pattern, for example.
But let's say none of these things have been arranged: the most likely situation is that I'm sitting in place alone, unaided, merely willing the mango to somehow appear in my hand through no great effort of my own.
That this should happen is improbable to the point of impossibility.
So, I review my options: supposing that I stubbornly stick to my original constraints (no gross physical movement), there is little to nothing that I can do to change the situation. To effect change, action is required; and only a particular subset of available actions leads to particular (desired) outcomes. If the set of actions-available-to-me happens to be disjoint to the set of actions-leading-to-my-goal, it seems I am utterly powerless. There must be overlap between those categories, otherwise it is logically impossible for me to achieve my goal through action.
Is there any other way to achieve a goal than through action? By the very nature of the word "achieve", I think the answer is no. Is it possible for me to accomplish something while doing nothing? Pace Laozi, the very idea reeks of contradiction. "But," I protest, "I am doing something – I'm thinking and simulating." The problem is that, apparently, thinking and simulating exert no influence on the universe if they are not accompanied by physical forces to realize their aims. Alone, they do not overlap with very many sets of actions-that-lead-to-goals at all.
How can I shape the universe to match my desires? Only through the channels that the universe allows me. And so the question becomes, how can I change those channels?