Why do we FALL in love?

I have been hearing the phrase fall in love ever since I can remember.
Why is it that a nice word like love has a nasty word like fall preluding it?
Its like we say " I fell sick/ill!"
If I just replace the words with their proper antonyms it would be "rise in hate."
Fall in Love and Rise in hate?
Getting the meaning?
I am going to try and explain it in ways I understood it.
The more I thought about it the more I felt that there is supposed to be a meaning for the placement of the words in this context.
When we are born we know less of the world around us and more and more as we grow up.
Do we then start loving the world more or hating it?
When we meet somebody and it is love at first sight apparently, do we know or do we think we know more about that person in just one day of acquaintance.
The point I am trying to make is that when we know less of something or somebody we are in love with it. The more we start to know or understand the same our love for it diminishes and hate starts to take its place. The adage "familiarity breeds contempt" holds very true here.
Now the words rise and hate, we fall because of less knowledge and we rise because of more knowledge.
So, when we fall in love, it is said that fools fall in love generally as fools apparently are fools because they just don't know anything. When they rise in hate, aren't they a lot wiser than earlier?
Imagine you are on a roller coaster ride and the feelings you have on rising and falling, while falling, due to the speed of falling we are at risk but we feel euphoria and love the rumbling feeling of it in the pit of our stomach. The moment we start to rise again the speed slows and so does the excitement.
While falling can be euphoric and offer a kind of sensation in one's life the ride back up is not at all quite appealing to my senses..

But all said and done one cannot rise without falling!! Can one?