What constitutes edge / why is my system working?

[panzerman]

Simple systems have becme well known. Professionals know that ameateurs use the simple systems. So professionals game them and eat amateurs' lunch.
I see it happen numerous times everyday.

I would think "Buy Low, Sell High" always stays profitable through time. However, since low and high are relative and not absolute (except for 0.0), what are some ways to differentiate the two? I use a highpass filter, but then I'm only break even as a trader.