That's truer than you realize even though it seems very simplistic and "cute".
This week try catching yourself whenever you start to worry. Pull up one of your "Kodak Moments" we've been creating (or recalling) over the past several months. Stop that worry in its tracks. But, since sometimes people have difficulty letting go of things, remind yourself that you're just doing this for "today" or "this week" if you're brave. Remember it's one step at a time. Take this the same way.
But look at what this picture is telling you - why would you want to destroy any possible happiness you can be having today by worrying about something that might not happen. It most likely WILL happen though, if you continue to focus on it (that's the Law of Attraction working quite well in your life even if you don't believe it is).
So, by not worrying today you accomplish at least two things. You divert your emotions/vibrations from the "lack" that you were going to worry about and possibly prevent it from coming. You also ruin your vibrations for right now and get your momentum started in the wrong direction. By the time you're realizing it, your car will be at the bottom of the hill and the momentum will NOT be able to be stopped. Try stopping it at the top of the hill. Then you can change the direction of your momentum easily. That's what we're aiming for when we want you to stop worrying about tomorrow as soon as you recognize that's what you're doing.
Try it, you'll like it. Let us know how it's going or ask questions about the best way to do this.