You forget things over time. We all do. But if you need to retain information for a test or presentation, you can be the Forgetting Curve with spaced repetition and engaged learning.

We forget up to 90 percent of what we learn within a week. But it doesn’t have to be that way. You can beat the forgetting curve and make your learning stick—for good.

Karpicke JD, Butler AC, Roediger HL 3rd. Metacognitive strategies in student learning: do students practise retrieval when they study on their own? Memory. 2009 May;17(4):471-9. doi: 10.1080 ...

Whether we are trying to master a new language or play a musical instrument, the pain of making mistakes is a big obstacle, especially early in the learning curve.

The curve is a simple graphic demonstrating how information is lost over time, but it proved that time-related forgetting is real (and has been reaffirmed by further study since).