High
Your attention leaves before the task is done, and this is far more obvious to you than to anyone watching. The thread drops, gets picked up somewhere else, drops again; work that needs long even focus takes you more time than it should, and you feel every extra minute. It's worth saying out loud what this level does not mean: it isn't about intelligence, ability, or how much you care about the work — people high on drift are regularly deeply interested in the very thing their attention keeps leaving. What is true is that environment decides a great deal. Open offices, notifications and work with no clear edge hit you harder than they hit others, and rebuilding your surroundings buys you more than trying to concentrate harder.
Moderate
Your attention holds while the task is worth it and leaves when it stops being worth it. This is the ordinary setting and a sensible one in most environments: sustained focus is expensive, and spending it on everything is neither possible nor necessary. The pattern usually looks like this — interesting work comes easily, dull work has to be negotiated with; on a fresh head an hour passes unnoticed, on a tired one it falls apart in ten minutes. What's worth watching isn't the level itself but what specifically pulls you away. It's usually the same two or three things, and they're far more often a feature of how your day is built than of how your head is built.
Low
Your attention stays where you put it. A task you start holds you to the end, a long piece of reading gets finished, a conversation doesn't lose you halfway through. It's a quiet, near-invisible ability — invisible right up until you sit next to someone who lacks it and the difference in what one evening produces becomes obvious. There is a cost, and it isn't about work. Steady attention switches badly. When circumstances change faster than the plan, you stay longer in what has already stopped being relevant, and you notice the new thing later than people whose attention was wandering the whole time.