This is when you find yourself staying up late to do something that seems like a good idea at the time, but you regret it in the morning. Most commonly this occurs during television watching.
Commedian Jim Gaffigan has brought this issue to light during his stand up routines. In particular, Gaffigan goes into detail about staying up late to watch a Growing Pains marathon. This seems like a great idea at the time, but upon waking up...Growing Pains wasn't such a good idea afterall.
So essentially The Growing Pains Paradox is staying up late for anything that seems like a good idea in the evening. However, due to the lack of sleep you regret the decision in the morning.
"Uggh, why did I stay up last night watching a marathon of Ninja Warrior? I hate The Growing Pains Paradox!"