Why Knowledge Has to Equal Proof or Certitude?

Andi: Some people have to make a conscious choice not to be that sceptical. Most of us don't, however, because we maybe are willing, at least to acknowledge some things. Yet theres also, when we're talkig about how these sceptical objections are sometimes presented,. There's the really strong form, which we just talked about, and i think pretty quickly we see that that's problematic. But there'se slightly weaker forms where people will say, well, you can't prove it, oryou can't prove anything. That might actually be the case, depending what we mean by proof, but that doesn't mean that it's still not an instance of knowledge