It's most likely designed with learning in mind. If you're getting a lot of wrong answers, maybe your brain needs a break. It also could be showing you shouldn't be advancing to the next stage.

When it comes to learning, your brain makes a lot of connections overnight. And if you overdo the learning, you won't remember a lot of it anyways. I've never had issues with not being able to proceed, but I also do two lessons over and over until I feel I understand it well enough to proceed since repition is a good way to establish the connections in your brain.