Self-discipline is also more costly. You can brute-force your way through tasks with ADHD, but it is more taxing on your overall energy. Those with ADHD typically experience impulses often and it's harder for them to ignore. Forcing yourself to ignore them requires extra energy. It's not sustainable to do all the time. It's hard for those without ADHD to truly understand what that's like.
In addition to impulsivity, executive dysfunction affecting starting tasks or work is also a big challenge.