Traditionally, an entrepreneur develops a detailed plan, finds money to fund it, and then pursues it to its conclusion. But conditions can change drastically at any point - you can end up locked into a process based on now-obsolete assumptions. The lean startup is all about agility and flexibility. Its mantra is "build, measure, learn": create small, experimental initiatives, get real-world feedback on them quickly, and use that data to identify what works and discard what doesn't. And then test some more.
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