this is a good question to ask and I had a long response that pc decided to have a brain fart and fail to post. too lazy to respond in full... so I'll summarize.

Hind sight we are looking at things from a disconnected and therefore more logical and rational view point so we see things we didn't see in the midst of the emotional high a new love gives us. Driven mostly by emotions, our rational mind typically ignores the obvious.

Driven mostly by emotions, our emotional mind typically ignores the logic and many times, obvious.