“Part of being careful is not to be excessively careful.”
If a person is excessively careful about not doing anything unless he is absolutely certain of success, he will not accomplish very much. While we should be careful not to take rash risks, calculated risks are necessary for anyone who wishes to utilize his potential.
Before taking a risk, list the pros and cons and weigh them carefully. But don’t demand absolute certainty before taking action.
Sources: Chovos Halevovos, Introduction; Rabbi Zelig Pliskin’s Gateway to Happiness, p.259