Imagine you rent a house. When you move in you start to bring in all sorts of items. The house is empty or you might say filled with empty space. As you bring in furniture the house starts to get filled but the space in the house remains empty. The space between the walls, ceilings and floors remains the same and stays unchanged.
Also you can take out anything that you had brought into the house. Again the emptiness of the space in the house is not affected.
Imagine your mind to be like the house and thoughts to be the furniture. Your 
mind like the house is filled with empty space. You can bring in thoughts but as with the house the empty space does not change.
At your choosing you can as with the furniture remove any thoughts that you have or thoughts that have arisen. Just take them out like trash from your house.
Neither the thoughts nor the furniture can move themselves. They are dependent on your will to move them in or out. Even furniture or thoughts that someone else caused to be brought in can just be tossed out.
Like spring cleaning, organizing your desk or deleting old email you can reboot or reset your mind to an earlier time. Perhaps the last time you were spontaneously happy. Why not? It’s all in your mind anyway. Just make up your mind to do it. Right now.
If not now when?
Spiritual Gravity 