Does hair really stop growing if you don't cut the dead-ends?

I'm constantly being told that if you don't cut off the dead-ends your hair won't grow any longer...I am kinda curious about this, because I am usually smarted than the average kid, but I was told this by one of my friends in cosmetology..and i know that hair is already dead, it's dead cells forming strands... it grows from the root (not the tips,because if it did when we cut it, it would never grow back) so how could not cutting the tips (or split-ends) stop your hair from growing...I would just like an answer to this so that my boyfriend in cosmo can just leave me alone about it already...