When I made post I didn't realize it was such a complicated question.
Yes, my examples could apply worldwide, but I'm asking about Italy, its ports, and its attractions.
Did you go to the Vatican an hour before it closed and felt too rushed and wish you had more time? Maybe an hour is enough time to see everything?
Did you regret renting a car and trying to drive to the Amalfi coast instead of just taking a bus tour there?
Did you book an excursion to see the tower of Pisa and wish you would have just done your own thing instead because you found it kind of boring?
Did you take the train to Civitavecchia but found it to be complicated and wish you took a taxi instead?
Maybe you regret not learning more of the Italian language because not as many people spoke English as you thought they would in a certain city?
I've never been to Italy before so I can't think of and list every possible example ever, so I'm relying on experienced travelers to share theirs.
If you've been to Italy and everything went perfect and you had a wonderful time, that's great. I hope that's my experience too.