If you are afraid to start up something, it means you have no real passion for it. When you have the luck to know what you really love, you must do it: play violin, a professional sport, cooking, ... or starting up a company to make a meaning, solve something that is wrong, changing the part of the world you do not like.
The reward is doing what makes you really happy; the risk is failing while learning and doing what you most like, if you have this luck, to know what you really love.
Steve Jobs in his famous speech at Stanford reminded us we all will die one day, thus any other risk is minimum against this certainty: nobody will escape this fate.
Thus, failing, making the ridicoulos in a public performance, bankrupting your start up, ... are all minor things versus our sure death: failing is the best that can happen to you, sometimes.
There is a famous spot by Nike where Michael Jordan, probably the best basket ball player in history, reports how many free shots he missed, how many points he failed, over and over again: this is why he succeed.
Life is too short to spend it in doubting: if you have a passion, just do it: what is the worst thing that can happen to you? Is this (low) probability worst than sure death?
You are marvellous, your life is marvellous: please do not spare it in a job you do not like, in a life it is not yours but somebody else's.