A Conundrum

I have recently been confronted with and once again failed to answer one of life's great mysteries: How does one pack light? The answer seems simple: Just pack what you need. But how do I know what I will need? A hundred different situations could arise, each requiring its own unique combination of clothing, toiletry items, electronics chargers, and miscellany. And though I'm not a boy scout, I like to be as prepared as possible whenever possible. So, I sit in the El Paso airport knowing I probably packed too much. As usual. Any enlightenment on this dilemma would be appreciated.