"For some, being rejected at all is a huge blow to ego, confidence, and self-esteem, which can have serious effects on mood and productivity, for instance. For these people, getting rejected more often means that each rejection is less significant and reinforces the knowledge that rejection happens."

Yes, but this sort of "therapy" only works if you have the right thought patterns to go with the rejection (i.e. not taking it too personally, realizing it's not that big of a deal, etc). It may not work so well if you (were raised to) believe that you have to please others in order to feel good about yourself. In that case, each rejection is just more evidence that "you suck", and you enter a downward spiral.