I made this mistake and I’ve heard of so many people who made the same mistake. What is this mistake? It is that many first-time visitors to Italy (and probably to other countries) try to pack in far too much. As a result, they have sub-standard visits to interesting places and they risk getting very stressed. Less is more. Take your time and plan an itinerary that gives you breathing space in each town you stay, each monument you visit and every meal you eat.
Finding the right rhythm for your visit is vital to your experience. And a good experience will encourage you to visit again. And again.