I’ve observed this for quite some time now which I think it can be safely concluded that:

The amount of happiness relatively equals to the amount of the sadness.

Life itself feels like roller coaster ((OOT: kinda remind me to Incubus’ wish you were here)). Once you climb to the top of the track, it tends to bring you down to the bottom of the track. However, once you got to the lowest point, it’ll climb back the track, vice versa. Hence:

1. Don’t be too happy when you’re happy.
2. Don’t be too sad when you’re sad.

As this famous persian adage ((Which I have posted before on this blog. Hat tip to Hafiz for told me the adage)) says:

This too shall pass