I appreciate your thorough response. I was questioning the usage of the phrase "know 100%" because I'm very curious about the relationship between "knowing" something and "believing" something. I would argue that there is no such thing as "knowing". And, I think this is an important distinction to make because the common view is that science is somehow fundamentally different to faith, and so we can magically trust it. Actually, science is simply the presupposition by faith that one's senses, mental computations, memory, and experiments are accurate. That's not to say that there aren't qualitative differences, but fundamentally it still rests on faith.

To the extreme, we don't 'know' that 1 + 1 = 2. In fact, you can't be quite certain that you just read that equation correctly. Or perhaps, after you read it your memory (mental or computer) was corrupted: it actually said 2 + 1 = 2.

You believe that 1 + 1 = 2. First, you believed it because someone told you (you trusted your ears). And then you reasoned about it for yourself, and you saw how if you have 1 object and another 1 object and combine them, then you had 2 objects (you trusted your eyes). And eventually you figured that this equation is perfectly knowable because it a metaphysical truth, but you still had to trust your mind to be infallible for that. Even if we believe 1 + 1 has always equaled 2 in the past, we have to take on faith that that is still true in this moment.