Most spaced repetition systems ask you to rate a card on five or six levels. Lingo asks for three: again, good, easy. That is a deliberate subtraction, and it is worth explaining.
A scale you have to think about is a scale you stop using
The moment a grade needs deliberation — was that a 3 or a 4? — the review has stopped being about the word. You are now doing bookkeeping. And bookkeeping is exactly the kind of small friction that turns a daily habit into a thing you did for a fortnight.
Three grades map onto what you actually know at the moment of recall. You missed it. You got it. You got it instantly. There is no fourth state worth reporting, and the finer scales mostly collect noise from people guessing at the middle.
The scheduling still does the work
Underneath, the intervals move the way you would expect: a miss pulls the item close again, a good answer pushes it out by a growing step, an easy one pushes it further. The queue puts overdue items first and fills the rest with whatever is new.
You do not have to tune any of that, and there is no streak to protect. Sessions are meant to be five minutes on a phone. A five-minute session does not want a five-button scale.