I often see people claim that we treated a player badly, or a player's career completely ruined because they were with us for two or three years. So two or three years can ruin a fifteen year career? It's such drivel. There are very few players that decent clubs let go that come back to haunt that club in question or prove them wrong. And even then it's normally a case that the player himself has grown up mentally or takes things more seriously or that he excels in some new role (usually placed there by accident due to injuries, suspensions) at a different club.
From Spurs I can only think of one modern day example, and that is Peter Crouch. There hasn't been another talented youngster, fan favourite etc. that we've let go who has gone on to prove us wrong elsewhere after we've willingly let them leave. The same applies to the other "big" clubs. How many players that flop at those clubs go on to do well elsewhere? And it's not because those players were ruined, but because the players couldn't cut it at those clubs because they didn't have what it took.