As a jungler...
How do you explain nicely to a feeding mid that he/she is a lost cause for ganking? I'm not (as a 0/0/1 jungler, assuming) going to try gank a +3 levels and 1 big item enemy mid laner while I still only have blue smite, one ap book and boots knowing that he's going to be useless for damage as well.
Counterganks at this point would be deadly. To me, it is more strategically sound to try get the other lanes fed and come back as 2 or 3 to gangbang that now cocky mid.
The problem is, every time I try to explain that... they get defensive and start playing the blame game. I'm not even trying to blame anyone, I'll even admit that it might be my fault for not coming earlier. But how do you get them to understand that I'm NOT giving blue buff and I'm NOT coming to gank, but I WILL return when I'm capable of taking on the fed guy?