Or a too hard course. Or a bad lecturer. Or you skipped the previous lecture and it's all gibberish again.
I have literally never used anything I learned on that part of the course however.
I'm doing this course as part of the requirements for a degree in Eng. Technology, focusing on Software. It's common to all streams, but none of the subsequent courses Software students have to take will use this material. Damned if it isn't fun though.