We've all grown up with a version of the first quote!

"Conscience is what makes a boy tell his mother before his sister does."
-- Evan Esar

"Here's a rule I recommend: Never practice two vices at once."
-- Tallulah Bankhead

"Every composer knows the anguish and despair occasioned by forgetting ideas which one had no time to write down."
-- Hector Berlioz

"Eternity's a terrible thought. I mean, where's it all going to end?"
-- Tom Stoppard