We've made a few mistakes, especially on our earlier trips, like staying off-site or booking an expensive package. Our biggest mistake, though, occurred about 2 years ago.
We had decided to visit Universal before staying at a Disney resort and visiting the parks. So, we bought 3 day passes and stayed at Springfield Suites near Downtown Disney. We went to Univeral the first day and it was okay. The 2nd day, we went to IOA and couldn't wait to ride the new Mummy ride. DH, being a pooh sized guy, asked an employee before we boarded the ride if he would have any trouble. The employee didn't think so. However, when we went to sit on the ride, DH couldn't buckle the seat belt. The attendant made it difficult for us to get off of the ride and it turned into an attention drawing scene. That was very embarressing to DH and upsetting to us. We were so disgusted, we ended up dumping the rest of our ticket and went to MK. We couldn't add on to our Disney tickets because they were special ones we bought to attend a sporting event. We really felt like we had wasted time and money.