Confidence is "I can" do psychological condition, is a necessary condition for success.

自信是“我能行”的做事心理状态，是成功的必要条件。

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Says Kirk: "Failure early on is a necessary condition for success, though not a sufficient one."

柯克对《福布斯》杂志表示：“早期的失败虽然不是成功的充分条件，但却是一个必要条件。”

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Yet that is a necessary but not sufficient condition for its success.

然而，对于它的成功来说，这是一个必要条件，但不是充分条件。

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But sex appeal for the male athlete is neither a necessary nor sufficient condition for endorsement success.

FORBES: Selling Sex In Sports Creates Opportunities But Demands Responsibility

Having a mastery of a particular function such as finance, support, marketing, or engineering is a necessary, but not sufficient, condition for success.

FORBES: A New Era -- the Era of the Customer