I am reading La Peau de chagrin
and I wrote this down the day before yesterday or so (though it's probably on a million quote sites):
'Vouloir' nous brûle et 'pouvoir' nous détruit, mais 'savoir' laisse notre faible organisation dans un perpétuel état de calme.
Spoken by a character who is 103 years old of course.
I find it a struggle sometimes to read French literature bc a lot of French authors love repeating the same thing over and over, no matter what century. But, at the same time, it's where the best quotes are to be found.