Bonus tip:
A distinction that I often find useful is that "simple" is not the same sad "easy". Biggest example of this for me was when I needed to go no contact with a family member; despite knowing that it was what I needed to do, it took me a while to muster the strength to do what was necessary — it was simple, but not easy.
Another manifestation of "why didn't I do this sooner" is when a solution is easy to implement, but it took a while to figure out what to do — this applies in complex situations, or ones where I have made past attempts that have failed, and I need to work smarter, not harder.
Both of these problem shapes benefit from the motivational interviewing technique described above. I think whenever we're thinking about ways to improve ourselves, it can be easy to slip into a pattern of being unkind to yourself. Some things take time and that's okay, because it needs to be — you can't bullying yourself into change.