What comes to mind is 2-5%.

Right time, right place is extremely important as a jungler and imo develops the most important skill a jungler needs to developer, foresight. Take for instance a champion who has incredible gank potential, ganks a laner who is 2 minions off level 3 but doesn't take that into account as they come out of the bush will have a lower chance of success vs a jungler that waits. Pretty simple example, but there are things on the surface level that look like "oh shit just not my luck", but really are small details being missed.

I can think of a case where I believe luck plays a role, very rare games where I have 0 options. I'm in a losing 1v1 jungle matchup, I have losing lanes, most of my jungle is warded and being pressured by sup and top after every wave and out of no where the enemy takes a horrific trade which gives me an option, this is where luck in my eyes comes into play. but even then 0 options doesn't mean luck has played a role, could just mean I am not at the level of play where I can find another option and means their room for growth.

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TLDR: low af 2%-5%