yes i have seen and experince it myself.. i introduce this group of friend of mine during form 1.. we started dota and got addicted to it.. and eventually we started to play more often... then.. we started breaking up into 2 groups..

1.The Good players
2. The not so good players

Then we started to train among each other.. One day.. while training.. this not so good player got tired of losing to the better players and started complaining.. then it all started.. fights and exchange of vulgar words... then 10 good friends from the same class.. become enemies by form 3... then.. we split.. now its just me and 3 friends of mine left trying to start a clan.. I regretted teaching the 10people DoTa...
-.-

yea... thats why... i did a big mistake.. really messed up.. as team leader i shud mix.. but i was sooo into the good team... because i wanted to build up the teamwork... but it was a big mistake.. regretted...