"Quotes"

Part of improving yourself is fundamentally denying impulses and habits you're used to from before. Eating healthier can be fun and taste good, but you still suffer cravings for junk food, or now that you're eating smaller portions only until you stop being hungry—instead of until you're stuffed—theres a minor amount of suffering to that.

Wanting to get better at socializing means making a lot of mistakes that can be humiliating. You could even have your mistakes recorded and posted online for millions of people to laugh at.

It's hard to say how you'll suffer, but improving your life and being a better person costs you something even if it's just the comfort and familiarity of how you used to be. The magnitude of suffering and how often you experience that varies though. And it's balanced by things being better like being more flexible, strong, feeling or looking better, being able to speak publicly or to people you find intimidating.

Fundamentally though you are literally carving away familiar parts of you to shape yourself into a different person. That change from habit is enough for people to call it suffering. You'll likely pine for the way things used to be. A married man with kids might sometimes wish he was living a simpler life as a bachelor, but also know their life is better with their wife and kids in their life.