Here's a good summary list by Tom Tunguz (a VC at Redpoint Ventures) of the risks that VCs typically consider:
Market timing risk
Business model risk
Market adoption risk
Market size risk
Execution risk
Technology risk
Capitalization structure risk
Platform risk
Venture management risk
Financial risk
Legal risk
Some of the above risks have been widely discussed and understood by entrepreneurs. However, some startups probably haven't thought through some of these risks (e.g., venture management risk) before raising venture capital.
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