The first year of life is (ideally) about unconditional love. But note what this turns into: the mood swings of "the terrible twos."
The next stage is about conditional love – which tends to lead to greater emotional stability.
In "adulthood," I’ve seen men essentially trade "emotional heroin" in return for "sexual cocaine" from women – which leads back to the terrrible 2’s again.
The lesson: unconditional love is a drug, use it like a doctor, not like an addict.