People shouldn't just accept this sort of thing as normal. You're paying (in the US or UK anyway) a lot of money for a degree level education. That means it needs to be fit for purpose, and if you're not learning then it isn't. You need to stop the lecturer and ask them to go over the point you didn't understand, or ask for additional time after the lab, or at a push, make a complaint to the course leader that the lecturer isn't teaching you well enough.
Learning to stand up for yourself and ask for what you need is a big part of the university experience.