On the subject of risk coming from not knowing what you're doing, I'll have to go with "it depends" on that one.

Yes, not knowing what you're doing definitely increases risk. If you try to drive to work, and you don't know how the brakes work, you're more likely to end up injured/dead than to end up safely at work.

On the other hand, there just simply are no valid ways to know some things that can tremendously increase risk. Not knowing a small meteor is about to land where you're standing right now definitely increases your risk, but there is simply no valid way to know that's going to happen.

Also, as mentioned, there's no way to learn new things without taking some risks. You just have to do your best to mitigate the risk and maximize the gain, but the only way you'll ever expand your horizons in any way, is to take some amount of risk.

The worst risks, however, generally come from people who think they know what they're doing, but really don't.

Honestly, I like to periodically do things that are crazy risky, just to push myself. If what you're doing is free-style cliff climbing, no matter how much you know about it, no matter how much experience you've got at it, you are still at risk every time you practice that skill. I think that's a necessary part of life - taking risks just for the gain of knowing that you faced a risk, openly, knowingly, and went, "sometimes, you just have to say, 'what the @$%^'".