"Discipline equals freedom."
--Jocko Willink and Leif Babin, Extreme Ownership
"Hard choices, easy life. Easy choices, hard life."
When you're faced with a choice between an easy option and a hard option, your default reaction should be to take the hard choice.
I'm not saying you always have to take the uncomfortable choice, but it should be your default, only to be deviated from with good reason to do so. You need to get comfortable being uncomfortable.
As you seek out short-term discomfort, slowly but surely, piece by piece, you start accumulating all these small advantages. You get a little healthier. You get a little smarter. You get a little more done. You grow as a person. You build the decision-making muscle that eventually means you no longer find it difficult to make the hard choice. You've internalised the idea that the second-order effects are much more important than the first-order effects.
These small advantages are individual snowflakes, accumulating into your snowball, that starts off small, but slowly gathers mass and speed, until you realise one day: it's unstoppable.