Do not feel absolutely certain of anything.
切勿认为任何事物是绝对确定的。
——《在沪举办茶话会上的演说》(1916年7月17日)
Millions saw the apple fall, but Newton asked why.
睡得早起得早,使人聪明、富有、身体好。
No man's knowledge here can go beyond his experience.
Quality is conformance to requirements, not goodness.