The pattern where balls follow one another
over the top, and then get passed from one hand to another underneath. This is not
the easiest juggling pattern, but it is the one most well-known to the non-juggling public.
You may be able to learn this pattern by starting at the Half Shower and making the underneath throw shorter and shorter and faster and faster. However, you may have more luck simply by starting from a cold start.
But don't assume that the three ball shower is easy. (Although some people find it easier than others.) If you're already doing the Mill's Mess or four ball fountain or anything like that, then yes, you should learn it. But if you're still at the over the top stage, you might want to give up for now. Don't worry, you'll learn it sooner or later, and by the time you get to learning to juggle five balls, you'll be absolutely sick of it!