What i think a jungler's job is after maining jungle for 5 months.
Long story short i used to main Mid and Top but the tank meta and ADC meta made most of champ pool kind of Meh, mid i can only play Syndra now, top i have several options but i feel their less optimal so i became an Evelynn main(since i love her, maining her for 5 months now, yes that means before the rework.)
After transitioning to Jungle and Mid(it takes awhile) i found out what my job is, you see a problem start and it's your job to fix it before it becomes too big. That's what i think my job is, with Evelynn lately i'v found my teams going 4/0 6/0 before i can even gank properly but i always swing it back and end up with games like this one.
https://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2659590974/231258967?tab=overview
This one wasn't as bad early on just Klepto Gangplank was 3/0 and pretty early on in the game putting my team at risk, klepto gangplank is super scary if he get's where he wants to go but here's the fun part. I ran bot lane real quick, cause they were having some problems too, they just couldn't finish a kill cause of Sion, so i flashed under tower and killed the sion with my Ulti the second i hit six, eliminating their problem just long enough for them to make Vayne to far behind. Then i gank top, only needed to do it twice and top lane was fixed, mid wasn't an issue, now all i had to do was protect them, so i counterganked Kha'zix when he went bot lane every. single. time.
I eliminated all of my teams worries in the span of about 5-10 minutes, causing the game to spiral out of control as a result and making it completely unwinnable for the enemy, this is in my opinion what my job is.