They prove wonderfully effective at first, only to dwindle into uselessness.

刚开始效果都非常不错，不料后来竟渐渐失效。

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He implies that all experts have their seasons and then dwindle into irrelevance.

FORBES: George Gilder Is On A Ken Fisher Kick

The risk for Mr Venizelos and Pasok is that, having already lost so many votes to radical leftists like Syriza, they will be seen by the electorate as synonymous with the right, and may dwindle into insignificance at the next election.

BBC: Profile: Greek Pasok leader Evangelos Venizelos

The dilemma for Paris has been painful: to intervene - and be caricatured as a throw-back to the neo-colonialism of "la Francafrique" - or not to intervene, and see a first chance to stand tall on the African continent dwindle into the desert sands?

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