Overpacking for 7 days in Italy (Rome + Florence) — how do you actually pack light?

Next month, I'm going to Italy (Rome and Florence) for seven days. I'm trying really hard not to overpack, but I always do the same thing on every trip.

The last time I went on a one-week trip to Spain, I packed:

3 pairs of shoes → used 1, extra clothes → didn't wear half, and random "just in case" stuff → never touched.

I ended up dragging a heavy bag through trains, cobblestone streets, and small hotels that didn't have elevators. It wasn't fun.

I've already tried to cut things down this time:

planning 3–4 outfits that can be mixed and matched, only bringing 1 pair of sneakers and maybe 1 extra pair, and leaving out most "just in case" items

But I still think I'm packing too much.

For the record:

7 days in total, mostly walking around the city and taking trains. Staying in the city center, no car, and only carrying on (trying).

Questions:

What really helped you pack less for trips like this?
Is there anything you always think you need but never use?
Am I going to regret only bringing one pair of shoes on this trip?

I'd love to have some real experiences; I obviously haven't learned my lesson yet.