Make it or fake it." - same idea - if you're good enough at
   pretending, nobody will know the difference. Or "Be brave. If
   you can't be brave, act brave. Nobody will know the difference".
   all old versions of the same thing although "be good or be good
   at it" is more about "being a good person. And if you can't be a
   good person, be good at pretending to be good so nobody can see
   the bad things you do." I think that line was used in a few
   songs. "