Not that it sounds like you need it, but I just wanted to provide a counterpoint to the anecdotal evidence. I went to a UC school, and I only knew a handful of people who took longer than four years to graduate (among all of my friends/acquaintances at my school and at multiple other UC schools). The only people I knew who took longer than four years to graduate did so because they failed required classes and needed to retake them (engineering major so they needed to take all of these classes in sequence; they only took one class in their final quarter), took the minimum amount of units to be full time, double majored/minored (they could have graduated on time if they only did one major), changed their major late in the game (junior/senior year), or had to take a medical withdrawal (and a reduced workload in following quarters because of medical reasons). Everyone else graduated in four years (or earlier). I don’t know anyone who stayed longer than four years because they couldn’t get into the classes that they needed. It may be a contributing factor for some people, but it’s certainly not the main reason.