My best personal description of it would be something like... my brain is constantly thrashing and offloading caches - with Ritalin the context switches still happen but the prior task doesn't get booted out of memory... so it's sort of like imaging running across a marshland, where every time you hit water you lose... the Ritalin might be like logs across streams, it isn't that suddenly you're always running across solid ground, you aren't constantly in single focus[1] but you can cross more of the marsh and reach the far side without getting wet.

There, that's my terrible analogy.

1. There's a flip side, staying with the marsh analogy, there are also some dykes someone built randomly in the marsh and it's really easy to run along those, and they're really comfortable... but they might not go to the far side of the marsh - but hey it's right over there and it'd be easy to get over there instead of trying to trudge through the marsh. Running on those dykes feels really good since you're definitely running, but you don't get to chose where the dyke goes and it might not be helpful for yourself to run along it.