累 stacks a field 田 over silk thread 糸: burdens tied and carried, one on another. Accumulation (lěi) and the tiredness it causes (lèi) — cause and effect sharing one character.
累 is modern China's most-typed complaint: 好累 ('so tired'), 累死了 ('tired to death' — hyperbole as lifestyle), 累成狗 ('dog-tired'). The lěi reading builds up: 积累 (accumulate experience/wealth). The viral phrase 累觉不爱 ('too tired to love') compressed a generation's burnout into four characters. Field plus thread: the weight we carry, stitched on daily.
Field work 田 tied on with thread 糸, load upon load — TIRED.
累死了 'tired to death' is said roughly a billion times a day in China. Nobody has died of it yet.