I don’t think sadness is the loss of happiness.
Happiness and sadness aren’t true opposites.
To be happy isn’t to live in perfect circumstances, but to choose joy and hopefulness no matter what.
Sadness on the other hand is a perfectly natural and healthy human reaction to loss or to tragic circumstances.
To be happy is a choice.
The ability to feel sadness is human.
Choosing to be happy while in the midst of sadness? That’s wisdom.