It took me too long to try cruising. Our first cruise was only 4 days long, because we were afraid we may not like it. We're sorry it was so short. Now it is our favorite vacation. I love the days at sea, because I can just relax - do only the activities I want. When in port, we can choose to go ashore (with or without a booked excursion) or stay on the ship. It depends on if we've been there before or not. If we've been there, we can decide if there's something new we wanted to do. Sometimes what's there doesn't appeal to us at the time.
The next cruise we are taking (next month) we plan to not go ashore, but just relax (haven't had a vacation in a while). However, we may change our minds on going ashore, because we are going to a port we haven't been to before.
My mother was the same way. My dad kept trying to get her to go on a cruise, but being afraid of water (she can't swim), she didn't want to go. He finally talked her into it and they haven't turned back! They once were on board a ship for 3 weeks and my mother said, "It wasn't even too long."