Translation:Everyone is uncertain about everything.
It took me all the way to this lesson to recognize 'on' is used to negate words, similar to 'un' in english. Onmogelijk = impossible (not possible), ongeluk = accident (not lucky), et alia.
I feel a more idiomatic way of putting this would be "No one is certain of anything".
in the hatchers world everybody's insecure
Maybe so, but you've changed two words by moving the negative. There's nothing ungrammatical or unidiomatic about Duolingo's sentence.
What a life lesson :) I'll have to keep this in mind