When Zach goes through that depressive teenage goth phase in which he starts wearing all black and writing non-rhyming poems about life's meaninglessness, may I recommend that you force him, at that time, to view his own happy, froggy-hugging baby pictures? 

In my psychiatry practice, I recommend this "happy baby picture therapy" to parents of moody teenagers all the time.  Through the photographs, the patient begins to appreciate that life has its peaks and valleys, but ultimately is about rediscovering the innocent pleasures that we adults have long forgotten.  The therapy consistently works like a charm.

Well, other than that one time where the kid got so pissed off that he stabbed his parents and torched the family home.  Because of doctor-patient confidentiality as well as pending litigation, I regret that I cannot say more.