What can never be explained......

The only thing that cannot be explained is human emotion and behavior. I am not talking about conditioning and the whole Pavlov's dogs thing. I am talking about why 2 people fall in love, why those 2 people are mates. Eventhough we all know what I am talking about, noone can explain the why of it. Why those 2, why not another person, why not the other twin? Is there some pre-determined mate for everyone? or are there 2 or 3 and you get who you see first? I don't think this will ever be explained.

I think the human is too complex and we might never understand it all, even many biological processes, we can't figure them out. The how, especially. We can understand the why on this one, simply because we see the consequences. Why do we use a seratonin reuptake system, but other neurotransmitters don't? Wierd....