Second most important thing...

Everyone knows the most important thing in any relationship is communication
The next thing is timing
Some say that people have the ability to fall in love with anybody. This is doubtful but feasible if timing is taken into account
Both people have to be at the right place in their lives to properly receive the other
sometimes you meet someone who seems great. But the timing is off

Of course I don't include love in this equation because we're supposed to love everyone anyway, so it's kind of moot