累 is an ancient Chinese character. Its traditional form depicts the accumulation of silk threads (田 "field" + 糸 "silk"), suggesting the idea of things piling up until one is weighed down — a vivid metaphor for fatigue. The character has been used to express tiredness since Classical Chinese texts.

In Chinese culture, admitting you are 累 (lèi) is extremely common and socially acceptable — even a casual greeting response. The phrase "好累啊 (hǎo lèi a)" is heard constantly in workplaces and schools. Note the important homophone trap: 累 has three readings — lèi (tired), lěi (to accumulate/pile up), and léi (as in 累赘, burdensome). Context always clarifies which is meant.