I firmly believe that only with true sadness experienced can true happiness be felt.
I firmly believe that without having experienced true sadness, one would not really feel what true happiness is.There has to be a balance, no one can be perfectly happy without experiencing sadness nor can anyone be perpetually morose.
.... you expressed the same idea earlier too. So, this sounds repetitive.
There is no relativity to it if you just experience happiness. To attain perfect balance, we have to experience both the extremes in order to feel the originality in both happiness and sadness.
Relativity exists only when there are two things to compare. Therefore, happiness being a relative experience, needs to be assessed against the other extreme of sadness. ... Now have an example to justify your reasoning. Otherwise it would not be interesting for the reader to follow.