An answer was given: "Try research. Science knows things.
And I got to thinking:
We can know certain things through research or experimentation. But all knowledge based on someone else's experimentation is ultimately reliant on trust in their methods and practice.
And even then a good conclusion to a good experiment has many caveats and limitations: "This is true in this case, but possibly not true in general." Thus the actual knowledge of any given study is narrow at best.
And then, if we were only to base our practical knowledge on what is proven in experimentation, then we'd have a hard time eating breakfast because different studies show different things in relation to the nutrition of eggs.
It seems to me, most of the time, life is just about thinking and assuming, not knowing.