If you look at the context in which I used that phrase, it was in reference to my own relationship with my boyfriend, not to all relationships in general. For me, he did indeed come out of the blue (and I am always thankful that he did) but for others, it likely won't happen. The idea behind what I said is that if you learn to simply live your life and straighten yourself out without being hooked on finding Mr./Ms. Right, you'll be a happier and therefore more attractive person. A month before John and I realized our feelings for each other I was discussing the issue of finding love and attractiveness with a good friend of mine. He told me that if you're always putting yourself down, you become unattractive in the eyes of others rather quickly regardless of how you appear physically. If your life is a mess, then you most certainly will have that unattractive demeanor.
You're right, and you're wrong. Forcing someone to dump a bad habit (smoking, drinking, promiscuity, whatever) is 50/50 on damage and benefits I think. Ultimately it's good for both people because it otherwise could get worse and make both of their lives miserable. On the other hand, the short-term effect is the "quitter" resents the "forcer" and might say or do things that destroys the forcer's confidence in the quitter, and thereby destroys the relationship. I guess it depends on the seriousness of the habit whether or not the relationship "weathers the storm" so to speak.
Personally speaking if I had a bad habit and John asked me to stop, I most certainly would stop it for him because I value our relationship very much.
Actually if you modify it slightly to say you should keep your senses open, but refrain from committing unwavering attention to the cause, I think your analogy is perfect. That is essentially what you're saying. If you find someone you might like, watch out for details that might point to them liking you back, but don't let that urge for discovery consume you. Doing so will make you unattractive (again, having nothing to do with physical attraction).
I hope that all makes sense...