…was die Liebe isst.
Eros is a function of irrationality over time multiplied by rationality. The larger the amount of irrationality which is crammed into a period of time (for personal rational-user benefit), or the shorter the amount of time in which irrational acts are performed (ditto), is how potent your eros is. As time goes on, eros diminishes.
Philos is a function of rationality over irrationality multiplied by time. However many rational gains you make versus the irrational sacrifices you make over a period of time, decides the quality of your friendship.
Agape is a function of time over irrationality. How long you can persist in making irrational sacrifices, even of a small nature, indicates the depth of your love. As time goes on, agape increases. Interestingly, the less irrational the acts over time, the greater agape is as well. How many pairs of underwear did your mom wash and fold for you?