It isn't, 0.999... is, but 0.999 is exactly 0.001 less than 1.
Exactly. That kind of slopiness makes this more confusing than it needs to be.
+0.999...
Without reference to the formal notion of limits in real numbers (invented in the 19th century), the expression 1=0.999... is meaningless. So one shouldn't be surprised at the confusion and dumb arguments surrounding it.
A friend showed me this "proof" that makes it easier to explain to people who aren't math nerds.
1/3 + 1/3 + 1/3 = 3/3 = 1
.3¯3 + .3¯3 + .3¯3 = .9¯9 = 1
I can remember arguing in middle school (I was 9) with my teacher that 0.999' was equal to 1. Sadly, at the time. despite knowing this as a fact, I didn't know any of the proofs.
Mind, I don't think they would have convinced her.