三天两头 (sān tiān liǎng tóu) - (Similar Structure, Different Meaning) Literally “three days, two ends,” this idiom means “very frequently” or “often.” Learners often confuse it with `三天打鱼两天晒网` due to the similar numbers. For example, “他三天两头迟到” (Tā sān tiān liǎng tóu chídào) means “He is often late.”