Scootch as needed.
One day I was watching my 2-year-old son build his toy train track like so: He would add one piece, then scootch the little Thomas the Tank Engine train across the new piece; then add another piece, and scootch the train over a tiny bit more. I was about to suggest that he build the whole track first and then commence train-scootching when I realized that this was exactly what was wrong with my whole life philosophy. Sometimes, you only need as much track as you take up, so to speak. Everything does not need to be completely planned out before you get the pleasure of scootching forward.