Is 20% better than your 80%? What causes you to seek the 20%?

The theory of the 80/20 rule is this: The most you can expect in a relationship is 80% because no relationship is 100% of what either party wants. But because of this, there is a void of 20%that is believed to be filled. Now when some go in search of the 20, they jeopardize the 80 they already possess. So in essessnce they are risking another 60 to satify their need of the 20. Is the 20 really worth it? How do you deal with it? Is love worth it? A friend recently said to me "do not make ANYONE a priority if they are unable to reciprocate." Were they right?