DH didn't understand the importance of being early/on time for ADRs until our 2 Christmas trips. Two times, he made us "late": the first, Cinderella's Palace breakfast on the day after Christmas. This was to be the highlight of our trip - I had tried 4 different years to get breakfast and was never able to. Because DH had dawdled, DD and I literally ran through the park to get there, and we were still 15 minutes late. A very lovely lady at the desk outside took pity on me - she could see that I was practically in tears, and promised to fit us in, even though she had already given our seating away. (I don't know if I'm the person that crisi referred to or not. If not, then the staff at CRT must be awfully patient and kind!)
The second was a very difficult New Year's Eve where we chose to dine at Crystal Palace and the only seating I could get was 6:30pm. Although we got there the required 15 minutes early, I stood in line for half an hour just to check in, which meant we were "late". We were left to the mercy of the seating staff - which meant a further delay, which caused us to miss seeing Tinkerbelle fly, which meant that the next time we went to Disney it was me and DD, we left DH at home! He has promised that, if we ever take him along again, he will not make us late for ADRs.