Whoever said “time” is spot on IMO. Time and emotional support. As parents, we want to fix everything right now. Well - guess what - life doesn’t always provide an immediate fix.
Time seems like a simplistic argument, but maybe your kid needs to feel rejection after working really really hard because that in itself is a very valuable lesson that will only be recognized with the passage of time.
Any parent that cares for their kids doesn’t want to see them in pain, struggling, fill with self doubt. However, they do need to figure out how to deal with disappointment, and the only class being offered on that topic is life itself. Furthermore, they need to figure this out for themselves. Doing everything for them - including fixing their problems - means they will never figure it out for themselves.
You can’t fix everything, but you can teach them strategies to constructively deal with disappointment and move forward - always forward.