I think he meant you shouldn't spend a lot of time thinking "Oh, I hope my competitor is not doing or thinking about doing <insert something you think would give them a big advantage over you here>".

I think some people use a strategy like: "Be good enough to eventually win over your competitors, but not good enough that they'll see you coming and decide to get serious at competing with you". I could see that happening at a startup trying to take control of a "secret niche".

I think that's an horrible strategy, it's like a glass ceiling artifically limiting your growth and progress.