I think we're not only all two-faced and fake at times, but that we have to be to preserve others' integrity.

Why think we've got the final answers in life when (as you say) sometimes we know we're just venting for our own reasons?

How often have we changed our minds later and felt the criticisms we expressed were incorrect or ill considered?

How often is the fakeness in fact for someone's benefit, as it would be if we give an insincere assessment ('Sure, that's a lovely dress') over something that doesn't matter?