There comes a point during the construction of nearly every piece of furniture you buy in which you swear that one of the pieces you got was wrong. You spend five or ten minutes flipping it around and paging through the manual, and then you eventually find out that you just misread the instructions and everything's okay.
Tonight, for the first time, I assembled a bookcase for which I actually did get an incorrect piece—the piece I got had the holes drilled on the wrong side. Luckily I'd purchased a drill in the last couple months, so I was able to fix the problem, but it was certainly frustrating. And now that sacred trust of assembly-required furniture has been breached. Now every time I assemble something, I'll no longer have that assurance that no, they didn't screw up, and I just need to figure out what's upside-down. This one little error will have permanently warped my mind to the detriment of all future furniture assemblies, perhaps for the rest of my life.