<p>There’s a lot of turnover during add-drop. Last year I and most of my friends were on the wait lists for various courses (we were all second-semester first-years with terrible registration times) - pretty much everyone got the classes they wanted eventually.</p>
<p>If you contact the professor well in advance to get on the wait list (i.e., not at the beginning of the semester, but during registration week), and attend the course during the first week of classes, you have a pretty good chance of getting in, unless it’s something extremely popular. You can even contact the professor before the class has filled, if you’re worried that all the spots will be taken before your registration time. In addition, if you’re not able to register for a course that’s required/important for your major (this happened to me), professors will often bump you to the top of the wait list.</p>