The biggest, most important problem to work on right now is any and every problem that's currently leading to the destruction of our planet's natural systems.

The biggest, most important problem to work on right now is any and every problem that's currently leading to the destruction of our planet's natural systems. Unchecked greed, rampant extreme inequality, resource abuse/waste, dis/misinformation, political extremism, all of the general stupidity that many (most?) of our richest, most powerful humans are guilty of encouraging/contributing to in the general populace of Planet Earth these days. If you can "increase user engagement" in anything that improves one of these critical areas, or anything related, you're doing humanity (and all life on Earth, really) a service.