Life is always about the most dominant urge. Whatever emerges as the most pressing thing - the thing that has to have attention NOW will be what dictates the next action.
Say you're engrossed in a book and you start to feel hungry, if involvement in the story is greater than the feeling of hunger then it will be ignored, until either interest wanes or becomes satiated, or the hunger pangs become too strong to ignore.
But what about will-power? Surely, it's possible to over-ride an urge for something?
For instance, you're working on something that you have to have finished by a certain time AND you feel ravenously hungry: you might think that you are able to exercise will-power by ignoring the hunger to get the necessary task finished. But the will-power is nothing other than the most strongest imperative; which is to finish the job, or suffer consequences which may be more dire than enduring short-term hunger. Conversely, if the hunger becomes physically unbearable, it may not be possible to ignore anymore and may interupt your ability to continue with the task.
Which points to the possibility that we are just a series of irrestistible urges. Urges that emerge due to numerous, uncountable causes: biological, hormonal, environmental, psychological.
What you are right now is the urge to read this sentence. A surging urge produced by an uncontrollable interplay of impulses, thoughts, feelings, sensations......
Just make sure you mop up after yourself!