Assuming what has been studied has been learnt
Assuming what has been studied has been learnt (or acquired) is an assumption, and may often be a dangerous assumption to make with learners.
Learners may not have learnt what they have studied because of ability, negative affect, inappropriate in the order of acquisition, there being a delay between studying and acquisition, language attrition, etc.
The real life consequence of this is that material has to be repeated, in different ways.
Textbooks and some courses often make this assumption, however.