Recognize that in an uncertain contest against Nature your instinct is wrong. Bigger potential rewards are not correlated with more risk. If you are pursuing a truly uncertain endeavor, like a startup, there is no way of knowing if the larger or smaller possible outcome is more likely to succeed, so the only rational course is to pursue the biggest possible outcome you can imagine.

Uncertain decision-making and the maxi-max criterion

Of course there are other reasons you might want to not pursue "the biggest possible outcome you can imagine" ... maybe you want to pursue the best outcome you can imagine, not just the biggest; maybe you have other constraints, like resources or your desired lifestyle.

Still an important insight - more ambitious goals are not necessarily correlated with more risk.