You know I didn't say that everyone plans 6 months in advance for Disney..not sure where you got that. I did however say Disney has a time-table for things (adrs, FPs). Of course there are so many people who do things on the fly...here's a hint I was one of them for my 2011 trip. We bought tickets a few weeks in advance back then

. You for sure don't have to tell me about being flexible and whatnot.
I don't care a ton about availability either. Disney has however said you need to book an ADR rather than being able to walk up (generally speaking) for sit down place. Of course you can book day of but Disney's time-table for that starts at 180 days which was my point.
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I know I either had this discussion before with you or others have pointed it out before but I really do think you have this notation that people vacation exactly like you. I went to D.C. and did some of the things you were interested in, I've been to Boston, I've been to Hawaii, I've been to NYC and what you described is not in any way how I vacationed or how I had to vacation. The only thing I had to book in advance was the White House because you have to go through your State Rep. I never waited to get into any museum nor Mount Vernon nor Arlington National Cemetary nor the Monuments at all and I was there in April, July (around the 4th too) and August. Never had an issue with Pearl Harbor touring nor did I have issues in Boston. Most of my vacations are history or beach too. Your statement "I can name 5 domestic locations off the top of my head that take more advance planning than Wdw" is way too much of a vast generalization which is why I commented. Those places take knowledge of what you want to do but not necessarily advanced planning.