I think if it's to be long lasting and healthy for both parties, then I think one needs a deep understanding of themselves. A lot of people go into a relationship to "fix" whatever they feel is "wrong" with themselves. To fill an empty void, to feel needed, to have someone to throw their attention on, etc. The best relationships I've had is after I've had my own shit figured out.
I don't want anyone to rescue me (and I seem to drawn in guys who like to rescue, given my current situation) and I'm annoyingly independent with a strong stubborn streak.
But I've found that relationships become healthier and more productive and have the ability to go the distance when you've met your own needs first and what your partner brings to your relationship is a benefit, not a band-aid. And on the flipside, I'm attracted to guys who have their shit figured out as well. Someone who is at the same stage in life as me.