If "everything" is simply interpreted as many things, I believe one can be great at something and good at many things. If you interpret "everything" as a vast number of things, then being good at a vast number of things is a greatness in itself. Peace is good, but I'm not sure this is the right application.
"Making peace with <x>" on a personal level is just "coming to terms with <x>" or "accepting <x>."
In this case, OP is probably accepting that he will never be a "master" or "guru" at something, while at the same time reaching "good" status on many things. This acceptance probably helps with not feeling that you are failing all of the time (i.e. not good enough) because you haven't reached some sort of "master/guru" status.
