The most common problem I see is technical outsourcing, there are a lot of MBA based teams who cannot convince a great technical person to join.

As a result, outsourcing to get the product done becomes a necessity and also easier than going around to find a good technical cofounder. It is also tempting since outsourcing seems cheaper and promises to get the product built.

The product just ends up not being good enough.

As a technical person in the startup industry, this is the #1 reason why I think startups fails.