Acquaintances vs Friends

Sometimes I wonder, how much effort should one put into a new friendship? I was having a chat with my colleague over lunch the other day, and we both agreed that in the initial stages of any
relationship, one really needn't have to try that hard.

It's all about chemistry, getting along and a mutual desire to deepen and strengthen the relationship.

As harsh as it sounds, I don't really need new friends. I have a core group of people around me that I know will always be there for me. People I love, value and treasure. It's the relationships with these people that I'll put in my utmost effort, and I know they'll do the same.

But once in a while you come across someone you think has the potential to be a good friend. However, if one party is obviously putting more into the relationship, especially at the beginning, it's not a very balanced relationship, is it?

So at what point do you draw the line? When do you say, ok no more. Or do you try to lower your expectations and just leave it be. When do you decide to stop trying?