When you've finally managed to tune out the rest of the world and get lost in your own thoughts, but still can't seem to focus, try the following:
Concentrate on the sound of your own breathing. Yes, really focus on it. Like, try to count how many times you can breathe in and out before you lose the thread of thought.
Read more on the Power of SilenceLook at your feet, really look at them. Notice how they're connected to your legs, and your legs are connected to your feet, and your feet are connected to the ground.
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