For me it is a big yes because we all know that being positive always give you the positive vibes too. Being a positive person always put you in a good situation. You must know how to act positively so that the outcomes of your actions are also positive too. And positive mind will give you the edge to have enjoyment and happiness while playing. But ofcourse be sure to know when to stop. 
I undertand what you meant. As someone lime me who strongly believes that the energy around us affects everything, it does make sense that we are attracting what we call "good karma" when we are thinking positively. This is usually what people call luck. They believe that they are lucky.
I am not sure tho if this can be applied in online gambling. Behind a provably fair game is math.
Anyway, there is no harm on believing in anything as long as you feel good about it yourself.