Attributed (falsely?) to Albert Einstein
No matter how thin the pancake, it always has two sides.
Xun Kuang, Chinese confucian philosopher:
不闻不若闻之, 闻之不若见之, 见之不若知之, 知之不若行之
Not having heard something is not as good as having heard it; having heard it is not as good as having seen it; having seen it is not as good as knowing it; knowing it is not as good as putting it into practice.
You should not stretch your legs beyond the lenght of your blanket.