In German, we have the expression "Mut zur Lücke", in English something like "courage to have a gap" - a knowledge gap. It is used between students, when they skip to learn something for an exam.
It's more the hope that this topic will be not part of the exam or test. So it is some kind of taking a calculated risk. The reasons can be diverse. Normally caused by the inability to understand or simply running out of time. Laziness or carelessness also play a role.
When someone says this, they stop learning (of a certain topic) and accept the risk that it maybe be asked in a test. Then of course they "knows their limits", but this is secondary. They are brave / have nerve to have a knowledge gap.
Is there a similar expression in Chinese? I even could not found a translation for "knowledge gap" in Chinese.