There are four types of people who sit before sages: (1) a sponge, (2) a funnel, (3) a strainer, and (4) a sieve: a sponge, which soaks up everything; a funnel, which takes in one [end] and passes through to the other [end]; a strainer, which removes the wine but collects the dregs; a sieve, which removes the flour dust but collects the fine flour.