Once, a long time ago, my mother was sitting with her group of close women friends. They were all musing about what made them sure that they would marry their husbands. The group seemed split in two. Half thought that their husband would make a great father, best friend and long-term partner. This half was highly practical in their choices. They chose based on their head and gut more than their heart. This is not to say that they had any less success in their marriages, but they weren't driven to marry due to passion.
The other half of the group WAS driven by exactly that, passion. They didn't really know if their choice was the smartest, or most harmonious, all they knew is they couldn't live without being close to this person. Kissing that person, and feeling the fire of passion that burned inside them, was the sole reason they just "knew" it was right. This group was led by their hearts and, um, other parts.
So, between the two types, which are you? Which are you inclined towards? Do you buy this theory? Are their other options I'm missing?