This one motivates person to at least try his best
A more truthful message would be, "You have much higher odds of being struck by lightning than of ever becoming president of the United States"
This one motivates the person to sit on his backside and do nothing.
My guess would be that if everyone was thinking in terms of "truthfulness", we would not have a civilization at all. After all, there's always more chances to NOT make a discovery than to make one, to NOT become the next Google than to become one, to NOT find a new continent than to find one etc.
And of course, he was going to miss a few blocks. But, suppose that everything else is equal - training, physical abilities, skill, and your opponents are ready to give it all and fight for each ball, while your teams is expecting to miss a few here and there - who would have better chances?