So, I've tried playing jungle several times, and I can do it of course, but since the jungle has changed a lot and you can't just powerfarm, forcing you to gank lanes, I find it hard to actually help my teammates. Whenever the enemy team has a good jungler, he's everywhere, he has presence, he can do anything. I don't feel like I can gank anywhere pre-5, even if I got an oppressively strong early game champion like Lee Sin(Not that I play him).
I pretty much play between tank junglers(Maokai, Sion, Rammus) and late-game junglers that can carry the game later(Master Yi, Tryndamere), and I can't seem to help my team enough.
I look at the minimap often, and most of the times I find myself pondering "Wait, it'd be a waste of time to go there, I'd rather get this camp" - And suddenly the enemy jungler is ganking my bot lane and gets a double kill, meanwhile I'm staring blankly at the raptor camp contemplating over my life decisions. And once I farm enough and feel like I'm a little ahead of others, I see that one lane has simply lost terribly, terribly hard, and occasionally flames for not getting a single gank, while being ganked themselves quite often.
Also, most of the times when I go in for a gank or something, it usually ends unsuccessful, therefore I feel like wasting my time, being level 3 and others are level 4, reaching level 5, and I get afraid of being left behind.
I'm not a beginner, I know how to jungle, I know how to gank, but I do not know when to gank and who to gank, as well as other reasons you may be thinking of right now.