Full Idea
As a rule we find pleasure much less pleasurable, pain much more painful than we expected.
Gist of Idea
Pleasure is weaker, and pain stronger, than we expect
Source
Arthur Schopenhauer (Parerga and Paralipomena [1851], XII:149)
Book Reference
Schopenhauer,Arthur: 'Essays and Aphorisms [from Pand P]', ed/tr. Hollingdale,R.J. [Penguin 1970], p.42
A Reaction
Never go on holiday with Schopenhauer. This is more accurate about pain, I think.