When should one switch jobs fast?

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Recently I was discussing with one of my friends how good is switching jobs quickly. My belief is that jumping jobs at the start of your professional career helps. At that time you are young, not quite sure of your goals, fresh to work atmosphere with perceptions and myths that are soon to be smashed. Fast jumps at the start help in determining what you are good at and what you like to do. After that you can stabilize in a job you find the best. My friend tended to disagree saying that quick jumps are a big NO-NO. You can only think of a switch or jump after spending a reasonably long time with one place. What are your views?