I am about halfway through "The Design of Everyday Things" by Donald Norman, a must read for most designers, and have found many gems to comment about. However, Norman's section on why designers go astray was the most thought provoking thus far. I'll summarize:
1. DESIGN community tends to place aesthetic first.
2. DESIGNers are not typical users. (they become expert on their product and don't believe other users may have problems).
3. DESIGNers must please their clients and they may not be the users.
Most of these aspects are still true in the design community. Aesthetic sometimes takes the front seat in the process.. I mean that is half the fun of design in my opinion. But Normans statement brings to mind anothe similiar statement I heard at IDSA conference, "A crappy idea well sketched is still a crappy idea."
I think every designer has experienced a short of tunnel vision in the design process in which we are convinced that an idea is correct. Even though it has been based many only on our perception. In my experience the incorrect idea is usually throw out the window after about the first couple of hours of users research. The extreme of this would be all those really bad/funny rejected entries on the "American Inventor" TV series.
In my own limited experience I have seen the lengths at which a company will go to please their client and it has a real effect on the finished design. On rare occasions, the client will want that exact prototype or rendering which is being presented. Even though the deliverable has been created within a minimal time frame and little research/time placed into it. Which places the designer in a hard to place to deliver the end solution under the constraints (size,cost,form,interaction,etc) of the first deliverable.