Full Idea
The man who knows nothing of ennui is still in the world's childhood.
Clarification
'ennui' (Fr) is boredom
Gist of Idea
You are stuck in the past if you don't know boredom
Source
E.M. Cioran (A Short History of Decay [1949], 1 'Dislocation')
Book Reference
Cioran,E.M.: 'A Short History of Decay', ed/tr. Howard,Richard [Penguin 2010], p.14
A Reaction
Boredom well may be the central experience of existentialism, rather than angst, or nihilism, or the temptations of suicide.