Between hindsight bias, fake causality, positive bias, anchoring/priming, et cetera et cetera, and above all the dreaded confirmation bias, once an idea gets into your head, it's probably going to stay there.

You cannot rationalize what is not rational to begin with - as if lying were called truthization. There is no way to obtain more truth for a proposition by bribery, flattery, or the most passionate argument - you can make more people believe the proposition, but you cannot make it more true.

Why does any kind of cynicism appeal to people? Because it seems like a mark of maturity, of sophistication, like you’ve seen everything and know better. Or because putting something down feels like pushing yourself up.

And someday when the descendants of humanity have spread from star to star, they won’t tell the children about the history of Ancient Earth until they’re old enough to bear it; and when they learn they’ll weep to hear that such a thing as Death had ever once existed!

There's something in science like the shine of the Patronus Charm, driving back all sorts of darkness and madness.

Through rationality we shall become awesome, and invent and test systematic methods for making people awesome, and plot to optimize everything in sight, and the more fun we have the more people will want to join us.

You couldn't changed history. But you could get it right to start with. Do something differently the FIRST time around. This whole business with seeking Slytherin's secrets... seemed an awful lot like the sort of thing where, years later, you would look back and say, 'And THAT was where it all started to go wrong.' And he would wish desperately for the ability to fall back through time and make a different choice. Wish granted. Now what?