Having to deal with the consequences of dropping a lifelong addiction most likely.

Quitting smoking fucking sucks. You don’t start to notice the positive effects of quitting for weeks after your last smoke, and you don’t realize until then how much the cigarettes are affecting your health. So it can really feel like you’re putting yourself through hell for very little benefit. When just having a cigarette feels like it can fix all symptoms you’re having now, it’s hard to keep going.