In my early years of learning about investing I spent a lot of time lurking and occasionally contributing to TMF Market Screens discussion group. I was really into due to my analytical tendencies, but couldn't ever lock into anything solidly. They just seemed to be Too Good To Be True. And they were.
Sometimes I think that the Bogle Indexing theory is just another market screen theory. Other (most) times I feel like it's the opposite of one. No matter which, I feel very comfortable with it. Mostly due to the goal - Invest diversely, at low cost, and be satisfied with the market returns. This isn't an attempt to blow everyone else away, it's an attempt to do as well as most without sweating the details too much. As we've seen, matching the market can suck sometimes. But I still think in the longer run it's the best way for me to go. And as someone famous once said, of all the market factors out there, the only one we can control are the costs.