To me personally, I find it difficult to understand when a bad guy is in front of you and you use your best move and miss let alone a critical miss. To me that's seems crazy, no way should you miss unless the bad guy has some crazy ass armor or is a higher level than you.
If you're talking about realism, this is why:
Yes, that maybe based on realism but what I'm talking about is someone who is new to DnD, it might seem difficult for them.