I've heard that a very high proportion of the economy is sales to businesses, but relatively few people who are thinking of starting a business think of anything but selling to consumers.
I'm guessing it's just that most people have little or no contact with selling to businesses, so it's a blind spot. There may also be an element of preferring to sell an obviously interesting product-- if you're selling to retail, you can still have that, but a lot of business-to-business products are infrastructure.
Thinking a little more, I think Joel Spolsky advocates selling to other businesses for much the same reason - they're fairly neglected and businesses are willing to pay a lot.
On Quora: What are some stupid things smart people do? Examples of common types of stupidity that are typical of otherwise very smart people.
Lee Semel's answer in particular would make a great post here: a "to don't" list. You may wish to go through and identify the cognitive bias or biases each is an example of.