Success in anything requires consistent effort. If we want to be successful in materializing our desires, we must first take control over our thoughts. We must control our thoughts continuously. We must learn to change our lifetime habit of thinking without focus or concentration. Although this includes no more daydreaming, it mostly refers to catching ourselves before we get pulled down into a vortex of negative thought. That's all too easy to do in this world of ecomomic and political unrest.
For the average person, daydreaming does not materialize thoughts idlely floating around in one's head. But, remember, everything is energy. So, idle daydreaming does produce karma, as karma includes any kind of activity. To create positive karma we must be aware of our thoughts and direct them in a postive direction. Yogananda recommended repeating a spiritual mantra, like "God, Christ, guru." when daydreaming starts to invade our minds.