When the demand exceeds supply. Your relationship will not last but if supply exceeds demand then it will.
P.S it doesn't mean that you spend a lot of money but spend less of it. Optimum uitilization of resources for maximisation of production. Same should be applied to your relationship.
The law of diminishing marginal utility.
First you crave for both the company and the love then you feel suffocated and cry for space.
Afterwards you can't tolerate each other.
Fixed cost- you take your girlfriend out on a date.
Variable cost- you girlfriend gets her younger brother.
