Don't start strong and finish weak - see things through to a good end.
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history
First recorded in Song-dynasty Zhu Xi's 《朱子语类》, where he criticized Ouyang Xiu's preface for promising much at the start but trailing off at the end - 'not stopping short of dragon's head, snake's tail.'
memory
Picture a creature with a magnificent dragon's head and a thin snake's tail - impressive opening, anticlimactic ending. Near-synonym: 虎头蛇尾 ('tiger head, snake tail'), which is more common today.
