What's the one thing that went wrong that nobody warned you about when building a house?

I remember when I was building a house, in all the excitement and overwhelming feeling of selecting everything, things can get quite messy. I wasn't always able to keep track of all the changes I requested/changes made by the builder,

how they executed certain things (eg: I requested 2.7m garage height and they delivered 2.2m instead), obviously an omission during the building stage but these were few things that I missed out on.

Just wanted to understand other people's experience on how did you keep track of all the changes, all the selection, all the changes signed off, if things were changed, making sure that the $$ were changed, if lets say you selected a different bathroom tile, the 1/16" grout you had selected elsewhere does not go with the new tiles etc.

How do you keep track of everything, what do you wish you had done differently during that time or you wish you had utilised the service etc.