> If you want to grow and push yourself you're going to need some new coworkers.

I don't think it's necessarily that clear-cut. Some individuals are capable of pushing themselves. Those who can't, may have managers who are able to. Or, perhaps they rotate to work on a different project or problem space.

One dosen't necessarily need to leave a company to experience change or extraordinary growth. Granted, the extra push/pressure may assist a bit.