Do you know why you make money in trading? Perhaps everyone would have different keys/factors/causes for why (s)he makes money in trading. Perhaps some of the keys/factors/causes are common ones to most profitable traders. Just perhaps! Feel free to post any of your relevant thoughts too!
I often hear people say what you said, "...until it does not work anymore". If it stopped working it could not have been based on the basics of price movement, could it? So it was not really a high probability, sufficiently tested, sound edge that could be expected to last forever. I would guess that the farther one deviates from the basics (gets far out on the limb), the greater the chances are of eventual failure, but not necessarily due to changes in the markets on which most seem to blame it.
I was speaking in general. A simple example would be option market making. I started in the business, options had wide spreads and were single listed. Now markets are fragmented with narrow spreads. The vig is gone. I had to move on.
@garachen had a good post about this, which i'm too lazy to find now. something about "what service/value is your strategy providing to the market?"
I don't believe I have an edge. Essentially I think I am just running a dynamic "alternative beta" portfolio, diversified across a relatively large set of assets. I earn a bunch of 'alternative' risk premia, eg momentum, carry. This doesn't require any skill, hence no edge or alpha. Why doesn't it get "arbitraged" away? Arbitrage is perhaps too strong a term, since it isn't risk free. Okay smart ass, why should you continue to make profits in excess of the risk free return? Because most humans seem unhappy holding portfolios exposed to these risks, and are willing to pay me risk adjusted profits in return. Will that change? Perhaps, but only if the medium term trading landscape becomes dominated by systems traders, or if human nature fundamentally changes.