hey backtrack a little. i know that there’s a chazal that says this. i’m not arguing that.
BUT, if you’re davening for the other person, but you’re doing it with selfish intentions that’s not davening for the other person – that’s davening for yourself!
when yitzchok avinu davened for rivka and was answered he was really davening for her – not for himself. that’s where this chazal comes from (i think!)
is that more clear? my point was, if you really have the right intentions – great. but if not you’re being an idiot.