That's a good point, but I think that that lesson would be better learned in the core-knowledge curricula (which the child's going through whether he/she likes it or not) than by wrecking his/her enjoyment of computer programming or violins or model-building or first-person shooters or whatnot.
So the child can learn that the limits of their ability are beyond the limits of their self-perceived ability.
We're talking about passionately applying oneself to an activity. This does not limit the locus to recreation IMO.