1) Well, you're on par/outfarming the other jungler, aswell as your level.
Timing is neccessary, e.g. you KNOW which lane might or/is going to get ganked thus you go to help that lane.
You've helped lanes win. <- most obvious one eh.
Objectives as a jungler, e.g. securing your buffs every game, securing drags etc.
2. This is so damn stressful and you can't always expect yourself to turn everyone around by yourself.
I don't think it's literally possible to save EVERY LANE. But you can help, perhaps 1-2 lanes and stick to ganking those. When you divide ganks e.g. you gank top, then mid, then bot. They still die even though you ganked. So focusing on a certain lane, crush that one then move on to the next can really benefit your team. Ward up for them <- this is very important. even though "im a jungler not the support" it doesn't matter. you still need to ward and this can make a very significant change to their lanes. Pink wards help for obvious warding spots for bot aswell.