[kanak]

Almost everyone registers for atleast 4 courses a term. You need to work on all of them because every course counts. However, when you're going to take the Junior Lab (if you're in Physics) or the digital death lab/ software labs (if you're in EECS), you take classes that are relatively easy. For example, you might take extra humanities classes to work on the HASS requirement and then in a later semester not take the humanities class and replace them with courses in your own major.

I don't know about the junior lab (i'm in eecs), but when I take classes that are difficult (which has been pretty much every semester for the past 2 years :(), I am working overtime on these classes. Besides attending lectures/recitations during the day, I spend every evening, and all of my weekend coding for the projects. Having projects and labs that took over 20-30 hours to complete were the norm, and in a particularly bad semester, I'd have one of those due almost every two weeks.

Initially, there would be people who could get by without putting in as much effort because they already knew the material, but as you go higher and start talking about lab classes (where the work is punishing regardless of your knowledge/experience) or graduate classes (very intensive, almost no one can coast), you don't see people coasting.