You gotta realize, in the real world most relationships do start with such an ambiguous reason. Just because I like your face, you were cute so I wanted to go out, I like talking with you and being with you so sure let's go out, we're compatible in bed so might as well keep it going, etc, etc.
The reasoning behind why they got together may be whatever, it doesn't have to be a fairy tale love story, what matters most is how they spend their time AFTER they start going out together, because that's what ruins relationships. False expectations, fabricated misconceptions, the idea that you know "Everything" about the other just to then get "betrayed", all of these are reasons why the relationship falls off. While on the other hand, you may start with something as frivolous as "I want them to stay with me, so I'm gonna lock them up while I can" and still spend a lifetime with that partner.
Love is complex and unique, hence why its so precious.