We've been learning about the Heisenberg Uncertainty Principle this year. It's true, ultimately we can't claim anything is a "fact".
Still, that belief gets us nowhere. If we want to make any progress, we have to assume that if a pattern occurs with no sign of changing, it will always continue that way. So for example, if all of us observe that things fall down when we drop them, then after years and years of observing this exact same behavior we can pretty much accept the notion that things will always continue to fall down when dropped. Building off of simple "facts" such as these, we can begin to figure out more complicated aspects of nature. It is only in this way- by observing, hypothesizing, and testing- that we can ever gather reliable information. By now, certain things have been observed so many times by so many people that we can pretty much accept them as facts.