A great time-traveller once told me

A great time-traveller once told me something I will never forget. I asked him "what was the most striking discovery you have ever made?"

He paused for a few seconds, dropped his usual smile, and with a clear shadow of disappointment in his eyes, he told me:

"That to save mankind and make it better, the obvious doesn't work. You must never eliminate threats, nor should you support heroes. You must do exactly the contrary. A sad thing to discover about our own nature".