A CEO of a very large, successful company said "execution is an order of magnitude easier than opportunity." In the context of young startups, I often feel exactly the opposite. Opportunity is everywhere, but execution in a bitch.
But then I thought about this a little. For a big company that dominates a market, it's totally focused on execution. The company is built for execution and, assuming it is built well, just cranks things out. What it cranks out might be inspiring, or it might not be, but it'll keep cranking things out.
In contrast, startups are totally focused on the new opportunity. Assuming they find it, and it's a big one, execution becomes the main challenge in front of them. Their activity is all about scaling up the organization, hiring people like crazy, building a culture of shipping great product consistently, reacting effectively to early customer feedback, and continuing to evolve their products to meet the new massive opportunity they are going after.
The focus on execution over opportunity assumes that you have an opportunity worth executing.
However, the line between the two is somewhat blurry. If you adopt the Lean Startup approach (which you probably should for many contexts), your startup is effectively an engine to discover an opportunity. And that needs to be executed well to function.
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