When you get good at driving, attention is freed for other things. When you get good at programming, the freed ressources you gain are used to speed up the programming. This speedup would, I think, not rollback without at least conscious effort and no other tasks can be attempted. The same should go for other skills whose effectiveness does/does not speed up with paid attention. If your desk job consisted of copying printed numbers into spreadsheets, you could probably divert attention after your input capacity is reached. If you were to juggle always as many balls as possible, you should never be distracted.