am I sure gravity exists? yes, 100% because I'm not floating off. Am I 100% sure there is "Truth"? no, but I'm reasonably certain.
Am I sure I did well on my test earlier today? Again, reasonably but we'll know the details next week.
Do I think I have the answers to the bigger questions? Nope. But hopefully I can use my mind in conjunction with others to come up with a solution that at least keeps us from getting killed.