And what would you rather we do? Not learn anything because it's not yet hard fact proven by years (or centuries, or millions of years) of scrutiny? Just because it's not proven yet doesn't mean that we don't have a ton of evidence suggesting that it is.
I'd go in and use Bayesian statistics to set up some sort of argument, but it seems unnecessary.
Not at all true. We understand an awful lot about the world. Except for a few parts of it, like the brain.
What we lack is certainty and objective proof. The very fact that we invoke the scientific method means that even if we're 99.99% confident that something is an accurate explanation, there's always the possibility that some test we haven't tried will invalidate everything that we know. Hence why we have to continue to test and retest. We don't do so to prove that we're right. We do so to show that we're not wrong. (Note the subtlety in the difference there.)

Yeah, and how to we know that we're real?