Love at first sight is actually more like lust at first sight. Humans are instantly attracted to someone on first sight but don't love them. The realization of love at first sight comes when looking back at that moment. It is likely someone has had that feeling before but since it didn't work out, it wasn't love at first sight as we know it. Relationships that result from that connection and work out well are love at first sight because they became love. Relationships like that include Dr. Drew's who loved his wife at first sight (not the other way around), exactly like me and my SO.
Another fact they mentioned is that women are actually less likely to have love at first sight than men! Men are much more visual so they are more likely to feel that sort of attraction or pull which explains a poll that was given. When it asked men vs. women if they believed in love at first sight, 10-15% more men said they did. Interesting, no?