Full Idea
Mill, in his crisis of 1827, asked himself whether he would be happy if all his objects in life were realised, and had to answer that he would not.
Gist of Idea
Mill wondered if he would be happy if all his aims were realised, and answered no
Source
report of John Stuart Mill (Autobiography [1870]) by Simon Critchley - Continental Philosophy - V. Short Intro Ch.3
Book Reference
Critchley,Simon: 'Continental Philosophy - Very Short Intro' [OUP 2001], p.43
A Reaction
The reply is either that happiness is in the striving, or that his aims in life were wrong, or that happiness is impossible. It seems to contradict Kant's definition (Idea 1452).
Related Idea
Idea 1452 Happiness is the condition of a rational being for whom everything goes as they wish [Kant]