I have a confession to make and it's one that I'm embarrassed to admit, but I feel it would be best to warn all of you with my experience. I just received my pass for SD today so I now feel prepared to share my story.
I failed SD on my first attempt on a single fatal error of a 20' dead end corridor. I nailed the interior vignette in 25 minutes, and finished the building layout vignette in about 2.5 hours. I knew that I had properly completed all of the building layout's requirements - windows, egress, adjacency, visual control, corridor widths, views, SF, orientation, corridor area... all of it. Without going into specific detail about my test, I screwed up on something so clear to me now that I have no idea what I was thinking at the time.
Here's my mistake: As a part of the program there was a space that's name sounded vague and not at all like circulation space, and it required visual control; however, it showed up in the drawing with the light yellow hatch that should make it circulation space. Thinking that the drawing had made a mistake (this was my huge error in logic), I treated it like a room. I put a door on it, I branched it off from the main corridor, and its dimensions were such that its depth was greater than 20'. As soon as I did this, it was a dead end corridor, and an automatic fail.
I was devastated when I got my report back and really pretty ashamed. This is a test that 80% of people pass and I had screwed it up on something that I would not have ever done 9 times out of 10. I was lulled into a state of over-confidence. I tried to be smarter than the program and that was just incredibly dumb.
So now that I've retaken and passed (!) SD, I humbly admit to my costly mistake. Take what the program gives you and work with it. This test is easy if you do not overthink it.
This forum was key in my studying, so thank you all for your posts and comments. For those that have yet to take SD, just keep reading and learn from others mistakes on the practice vignettes, remember your code requirements, and get fast with your decision making. Do some practice vignettes and post them here for comments. You'll nail the test.
4 down, 3 to go. Hopefully this experience will bring me a bit of wisdom for the last 3 tests.