Better self-control makes you happy

People with better self-control (or self-regulation, self-discipline, or willpower) are happier and healthier. They’re more altruistic; they have stronger relationships and more career success; they manage stress and conflict better; they live longer; they steer clear of bad habits.

Decision Fatigue

You have a finite amount of willpower that becomes depleted as you use it. Your will, in other words, is not a manifestation of your character that you can deploy without limit: it’s instead like a muscle that tires. From Deep Work by Cal Newport