I remember myself juggling for the first time, I was in our house's porch and juggled the whole day long - my back hurt like hell and I though I would never have success - I didn't manage to do more than 4 jumps of 3 balls.

yeah - you sometimes don't even notice it - but the practice do make you better! I didn't reach the level you describe in juggling but I am pretty handy with 3 balls, tricks and all.

I can't emphasize enough how much this block on block and returning to previously learned material while integrating it with the new materials is important - all I can do is give my example - I learn medicine and there are courses to which the study material for the exam is about 500 4A pages. now - you can't really study it all in the 7 free days they let us have before the test - what you have to do is study during the whole semester and integrate the whole thing together, not just among the course material itself but also with older courses from previous years.

so I guess it's the same for every profession and study - learn things again and again, and in integration with the new materials. usually it will make you understand everything better and you'll be able to deduce new insights on new problem you encounter, as you know the whole building that brought you to this new build floor.