TL;DR: the technique of spaced repetition can help you remember information extremely efficiently and reduce your review time significantly.
In order to become a U.S. citizen, I had to learn 100 facts about the United States such as how many amendments the constitution has, explain what the judicial branch does, and who the current Speaker of the House of Representatives is right now, to name a few. Learning 100 facts about a particular topic can make you quite knowledgeable which in turn can be quite fun. Not only did I pass my citizenship test with flying colors, but I also enjoyed being the only American at my friend's dinner party the following week to know what territory the United States bought from France in 1803 (the Louisiana Territory).
Granted, I had stressed about passing the exam and had spent several weeks memorizing all the questions, which explains why I knew those facts and my friends didn't. Moreover, it's now been over 4 years since I became a citizen and I'm ashamed to admit I've forgotten many of the facts I learned. It makes me empathize with my American friends who couldn't remember these facts either. We have such busy lives and our brain is designed to forget the things we don't use on a regular basis. It's not surprising most Americans would fail the citizenship test.
How I studied for my citizenship test is very common, however it is also not the most efficient way to learn for long-term retention. I acquired the knowledge through a few intense and focused study sessions (which is very good) and then stopped thinking about the information as soon as I didn't have any immediate use for it anymore (that's the bad part). Learning something takes much more time than reviewing something you already know. Having to re-learn something is both frustrating and time consuming, but thankfully it is also something you can avoid.
The trick to saving time is to practice recalling the information right before forgetting it, something known as spaced repetition. This is the most efficient way to remember things because you won't waste time having to re-learn things, which more time consuming than reviewing something you already know. Furthermore, because you are waiting as long as you can between review sessions it means you don't need as many of them. That's more time saved for you. Because of how spaced repetition works, review sessions become more and more spaced out over time. Based on a recent analysis of my own review sessions, I found that in order to remember 100 pieces of information forever I only need to spend 3 hours reviewing that information over my entire lifetime . The challenge is knowing when you should do a review session. Spaced repetition tools like Sapienza can help you with this by keeping track of when you are likely to forget something and prompting you to review that information just before it disappears from your mind. Doing these quick review sessions at the best possible time will not only make you remember the information indefinitely, but it also saves you a lot of time.