Gnip (a social media company) grew a lot in 2012. We did a lot a of things really well (we have an experienced, proven, management team), but I personally botched a least one thing.
I let certain aspects of process and reasons for doing certain things go unspoken, after initial conveyance, for too long. Some of this was conscious and intentional ("spread your wings and fly" kinda stuff), but some of it was not. Regardless, some key stuff drifted for too long, and when you have a room full of bright, passionate, driven people, they will find their own way no matter what's going on around them. That's, nine times out of ten, exactly what you want, but unconscious drifting from a tenant is not.
Beating others over the head with process or beliefs is obviously detrimental, but regardless of how much trust and confidence you have a team your scaling and building, it is still a set of people in a room that haven't worked in the new environment together before. Regularly checking in and sync'ing on the key stuff is imperative. Without doing so, key experiences and learnings might not be leveraged well during future challenges; right when they matter the most.