Buying a mil-spec Colt with the sharp rear tangs. It needed a beavertail which means a new hammer and trigger job. Of course, the plunger tube was loose and the empties were hitting me in the head. So, two more parts added.
Learned to shoot with my thumb on the safety, which means an extended safety and to get the full benefit of a "high grip", an undercut grip.
Started to shoot "better", then, I wanted better sights to help and of course, more accuracy...match bushing.
Of course, today, you can just buy a "standard" model from most manufacturers with all or most of these " features".