Generally, a trading strategy is effective for a certain duration which is a function of the environment, news etc. I am currently learning about basic strategies that are (or once were) used. Some include simple mean reversion or standard deviation approaches others use more complex methods like machine learning for example. I tried a simple mean reversion strategy on some live data I queried and it turns out that that the end of day results were positive. My question is, why haven’t these strategies (or this one specifically tried) lost all the “alpha”? From what I’ve learned in classes, strategies like this that are well known should no longer be effective.
Excuse me if there is something obvious I’m overlooking before asking this question here. Thanks!