Important assumptions that were integral to the firm's major decision

Do you know of two major company's do you know that have faced this sort of problem One has to be automotive and on must be a computer company.

# The major decision facing the company
# Important assumptions that were integral to the firm's major decision, but, in fact, led to a bad or wrong decision.
# Explain why it was a bad assumption, and what lead it to be used, in part as a basis for the decision
# What would you have done to test the validity of the assumption?

* What specific kind of research or testing or surveying might you have done.
Note sure that I even understand this one at all. So any help you can give would be a great one. This is for a cornerstone course on marketing that I took over 4 years ago. Please direct me in the right direction. Please include any references that you can provide. Thanks.