I hear these all the time:

    1. Non-zero sum
    2. Market efficiency 
    3. Everything is priced in 

1 only makes sense if you are the market as a whole (you are not), not the one who is making the more informed decisions.

2 is true and actually a good thing for trading. It means there will be less noise vs signals.

3 doesn't matter if you are the market maker or you know the patterns caused by the "pricing in" and react to them.