You need to make correct predictions many times on many different things to get significant returns from your initial seed investment.

That is not true and entirely depends on what your investment is. For example, in late 2012 in a move that was heavily telegraphed yen dropped from about 80 yen/dollar to about 100 yen/dollar. That's a 20% return over a few months and given that FX trades are heavily leveraged (typically at 50:1 or so) you could have made multiples of your initial investment.