But if you don't have a few paragraphs of your assumptions written down, how do you keep the 3 other people aligned on your basic assumptions and direction?

What do you do when people forget things?

4) Requirements are conveyed verbally, not through written documents. Stories are short "reminders to hold a conversation," not fully-fleshed out.

There's still something written down, just not massive amounts.

Personally i try break stories down smaller to avoid the need for large tasks which helps. I also try minimise the time between story creation and story development.

Otherwise I just communicate a lot.

Things get differently from what I invisioned, sometimes they're worse sometimes they're better.

You artfully interrupt them and always keep watch on what other people are doing!