[gwern]

The timespan of change doesn't matter; the question, as always, is whether the benefits outweigh the cost.

Now, the cost is approximately <5 minutes per flashcard to give you roughly 95% recall (more details: http://www.gwern.net/Spaced%20repetition#what-to-add ); so the question is, does not knowing something you could've put into a flashcard - the consequences of not knowing it, the time it takes to look it up, whether you will even know to look it up, etc - outweighs the cost of a few minutes' review over that time period.

I think for a lot of stuff this can be true: shell scripting is not going away in 20 years, for example. If you're programming in it routinely, a language you will use for only 10 years can be worth memorizing for a while. If you're using a tool every day for the next year, there's going to be a lot worth memorizing there too.