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  1. Those in a hurry should realise that speed is not a means to success in life.
  2. Those in a hurry should realise that speed is not a means to success in the life.
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When you are speaking generally you should not use the definite article so "Those in a hurry should realise that speed is not a means to success in life." is the correct choice.

However you should use the definite article if you are talking about one or more specific lives, for instance "Speed has been important in the life of Usain Bolt", "Speed is important in the life of a cheetah", "Speed is not important in the life of snails" and so on.

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