The one time I can think of that the President took a big risk that didn't pay off was when he attempted to negotiate a Grand Bargain with Speaker John Boehner. That one failed. But I also think that after all his talk of wanting to engage in bipartisan reform, he had to at least give it a go or prove himself to be yet another politician made of empty promises.
I suspect that Obama's risk-aversion is tied to his competitive desire to win. We've gotten a pretty big taste of that this week with the SCOTUS Obamacare decision and (even more so) with Congressional approval of TPA. The President tends to take risks when he has pretty well gamed out how to win. I'm reminded of this quote from Steven Waldman:
One can debate the extent to which these achievements happened because of Obama’s skills or his timing. I think his long view, maturity, and pitch-perfect sense of when to take the big risk (e.g., jamming through Obamacare after the Scott Brown election; invading Pakistan to kill Osama bin Laden) were major factors.That "pitch-perfect sense of when to take the big risk" is the reason President Obama almost always wins when he engages on something 100%. His opponents would do well to remember that.