This is gonna be a short one.
In essence: how do we know we're doing the right thing, that we're doing something meaningful, if it's right for us, or right for the world.
We don't.
There is no one true path, nothing that will bring joy 100% of the time to 100% of people. This can be sad, but I feel like looking up at the stars and contemplating meaning is a rite of passage for anyone aspiring to true fulfillment. What's worse than feelings of existential dread1, is waking up one day and having a crisis, finding out that everything you've done has been for naught.
Harness the feelings, use them to explore what makes you excited, what awakens the fire to exist within you. Out of all feelings, this may be the most supremely human, so embrace it and know you're not alone.
I'd define this as the creeping sensation that what you're doing is pointless and may not be worthwhile, this can apply to the present or thoughts of the future. ↩