This quotation comes French philosopher Voltaire, who understood that you can't ever really know anything. While the unknown may cause you discomfort, if you're so certain that you never question anything, you're bound to run into problems.
Photo by Patrik Jones.
We've discussed the benefits of uncertainty before. It not only keeps you sharp by asking questions, but it also allows for the sorts of surprises that can make life interesting. Knowing the outcome or answer -- or believing you do -- might seem nice, but it's ultimately not in your best interest. You can never be sure of anything. That may seem frightening, but it can actually be a great source of excitement and discovery.