Surely, Corkeyloo - the lesson you really need to teach a child is that they should do the best that they can, be the best that they can? If you tell a child that they have to be The best at anything, and they don't succeed, they can end up feeling worthless and a failure - not something anyone wants for their child.
If, however, you encourage them to work hard, give their best effort, and do their best, then they can feel successful even if they don't win - and you don't risk them feeling that they will be loved less/failures if they lose.
I sung in classical music festivals when I was a teenager. Sometimes I won, sometimes I didn't, but as long as I had done my best, my parents were happy.
Not every child can win - there's only one top spot, but every child can do his or her best - that's what matters.