To do something superfluous or unnecessary, which instead of helping, spoils the original effort; to overdo it; to add unnecessary details.
这项计划已经很完善了，你再提出那些琐碎的修改意见，只会是为蛇添足，反而让大家无所适从。
This plan is already quite complete; adding those trivial suggestions for modification would only be like adding legs to a snake, making everyone confused.
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