The first and most important concept is that our brain wants to save energy at all costs. If it can spend less, it probably will. Hence, our brain will mostly strive for what's easiest, simplest, and most efficient. (Related to TK P: Ability (Fogg Behavioral Model))
Related to that, our decisions are largely guided by the amount of willpower we have. Willpower could be described as the amount of mental energy we have to perform deliberate and non-routine actions such as reading, learning, working out, new habits, and so on. It's a finite yet renewable resource. Like a battery, every time we do something deliberately we have less of it and it recharges in our sleep. The harder a task is, the more willpower it requires. And once we run out of willpower, we return to our default, automatic, low-effort behaviorsālike water that fills the deepest areas on a surface.