There once was a professor of philosophy ...
I can't find a reference to the story, so here's how I remember it.
Two students were in the professor's apartment arguing that it was impossible to know anything with certainty. As the argument wore on, he invited them to join him at the cafe across the street for lunch.
Upon reaching the street, he pushed them in front of an approaching carriage. When they both jumped back he asked them, "If you didn't know that carriage was approaching, why didn't you continue across the street to the cafe?"
While it may be true in a philosophical sense that you don't "know" something, there's a point where it's close enough to live your life by.