In short, 13% of VC-backed startups exit for over $10M, 5% exit for over $50M, and 2% exit for over $100M, which is what I'd call significant.
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Besides, there are a lot of startup opportunities that pay market, so you aren't "investing" anything in the equity, it's a bonus over what you'd get paid elsewhere.
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Since there's a lot of assertion and not much data here, let's bring some in. After some quick research, this Quora article seemed to have some useful statistics: http://www.quora.com/What-is-the-truth-behind-9-out-of-10-st...
In short, 13% of VC-backed startups exit for over $10M, 5% exit for over $50M, and 2% exit for over $100M, which is what I'd call significant.
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Besides, there are a lot of startup opportunities that pay market, so you aren't "investing" anything in the equity, it's a bonus over what you'd get paid elsewhere.