What's the #1 most difficult philosophical problem/puzzle to figure out?

[Anonymous]

that really boggles the mind etc :-)

[strateguy632]

Here is one. When kids learn colors! Show 2 kids the page "with a color and say this is red". Did both see the SAME color in their 4 eyes? Or maybe one saw different but all the ones that are "same as that different" he calls red due to being same as what he saw?

[jshm2]

Depends. There are numerous types of paradoxes in various fields.

[Agape93]

Depends. The trolly problem stumps people, but utilitarian have no issue.

One that's interesting is Rokos Basilisk, or fermis paradox and the dark forest theory attached to it

[AndrésC64]

The problem of evil. But to be fair, it's only a problem for people with invisible friends normal people using logic don't have this problem because we don't have to justify the unjustifiable.