"but have you ever said to your kid “You should’ve put in a few more hours into the practice. You could’ve made the volleyball varsity you always wanted”? "
Why would I be deliberately hurtful like that to my children? Encouraging hard work and discipline upfront is a completely different thing from saying “see, you could have / should have done more.” Are you under the impression that the OP simply didn’t work hard enough to get into the Ivies he applied to, so his parents have a “right” to be disappointed?