More than 95% of the students are not fully aware of these aspects.
If you study a concept and are able to answer a question on that just with your own knowledge or logic, there is no need to waste time on revising it. For example, a student studying geography studies that Equatorial radius of earth is more than its polar radius. There is no necessity of revising another concept which says Polar radius is less than Equatorial radius because obviously it could be deduced from the first concept.
Many such overlapping concepts don’t deserve to be revised.
When to revise is dependent on the functioning of human brain. With reasonable variations, the functioning of brain of students is more or less the same. For revision, if they follow a fixed set of time frequencies determined as per the way neurons work, the information can be retained for a long time – often life time.
How to revise depends on the subject as well as the individual. More on this is taught in advanced course of Studynomics.