I'm currently pursuing my bachelor's in Mechanical engineering and I am facing this issue since a long time. I study a subject completely and then forget it overtime as I continue to study new subjects. I thought repetition could probably serve me well. But if I start revisiting a subject all over again, it takes a lot of time, and then I'm in the dilemma of choosing to revise a previously done subject or study a new subject.

How can I overcome forgetting without wasting much of my time?

2 Answers 2


First, and most important, there is more to learning than "remembering". Your goal in learning something like engineering (or math or science or ...) is competence in the field. That is, applying what you learn. If you can do that, then remembering specific facts (if that is what you mean) is less important and they are likely to rise to the top when doing applications.

Another major goal of an education is to gain insight into the workings of the field. How do the ideas fit together to form a unified whole. That can be just as difficult to achieve as competence, though they are related. And again, the facts will be implied by the insights, making them easier to recall, but also easier to look up in reference material as needed.

But, learning requires two things (as I've written here pretty often): reinforcement and feedback. Reinforcement comes through practice and it changes the brain. Feedback is to assure that you don't reinforce things that are incorrect. Most coursework is designed to provide these two aspects along with the presentation of material in a coherent way. For the "change the brain" idea see The Art of Changing the Brain by James E Zull.

But there is a way to enhance learning and enable retention that go hand in hand. Here is a description of something called the Hipster PDA, which is nothing more than a deck of index cards. The value in learning is that the creation of the cards and the revision of notes is in reinforcement. If you write things out by hand you get strong reinforcement.

But the added value for retention is that you can carry around with you at all times a few of the cards (10 - 20, say) and review them when you have a few moments; waiting in Starbucks, perhaps. If you write important ideas on the fronts of the cards, leaving the backs blank, you have a way to make notes when you think of things or see some relationships to other ideas. If you use different colored cards you can keep different kinds of ideas easily classified.

And, you don't waste any time at all. We all wind up waiting impatiently for things. Even carrying a notebook at all times is a big help. Bound notebooks (Moleskine) are very good for this. Date every page. Leave room for updates.


Tips for Remembering What You've Learned

  1. It's scientifically established that students will learn better when they like the subject of the class.

  2. It's also known that students learn better when they like their teacher.

Given these facts, even if right now you do not think you like the class or the instructor, try to like them anyhow.

It's a similar concept to getting more nutrition from a food you enjoyed. You will retain more when you actually like, value, and appreciate the subject matter.

Aside from doing your best to enjoy/think positively about the subject, it also helps to apply what you've learned in some way. Think about how what you are learning affects your life or that of others, or how it can be applied to solving problems, etc.

The Best Tip

But the very best tip of all (I saved the best for last) is this:

Teach it!

That's right--when you have begun to grasp the subject matter, find someone to whom you may explain it. When your mind is applied to the task of explaining what you have just learned, it is forced to organize your thoughts, which may still be somewhat sketchy, and to make sense of them. One cannot teach what one does not understand. Furthermore, the very fact of teaching it gives opportunity to repeat the knowledge and make a practical application of it to someone else.

  • Yes, the standard joke is that math grad students finally really learn calculus after being a teaching assistant for it 5 years in a row, and then teaching it another 5 or 10. And teaching first and second-year grad courses several times is what finally cemented my knowledge of that stuff. :) Commented Feb 21, 2022 at 22:10

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