In The Last Lecture, Randy Pausch uses the idea of the "brick wall" as a symbol of potential blockades or endings to dreams that he had. The point of his lecture was to demonstrate how creativity and perseverance can overcome such road blocks so that childhood dreams can be achieved.
For example: Pausch dreamed of experiencing zero gravity. When a college student team he advised won rides on the Vomit Comet used to train astronauts, he was ecstatic until "the first brick wall, because they made it very clear that under no circumstances were faculty members allowed to fly with the teams."
Later, Pausch relates the negotiations that went on before he was able to work with the Imagineers at Disney in developing the virtual reality technology that supports the Aladdin ride. His immediate superior at the University of Virginia, where he was employed at that time, was not supportive of Pausch using his sabbatical in that way. "Some brick walls are made of flesh."
There are others in the speech - any complication could be considered a brick wall, a challenge to be overcome.