Rebbe Nachman of Breslov teaches us :
You are wherever your thoughts are. Make sure your thoughts are where you want to be.
Make sure you don't allow your thoughts to become chometz--leavened. Don't dwell on bad thoughts or desires at all.
When a person purifies his heart and expels all unholy thoughts from his mind, thinking only good thoughts, he can bring about real miracles.
A person's entire destiny-for good or ill-depends on the thoughts in his heart.
If you allow yourself to be depressed about these kinds of thoughts (negative) it simply feeds them with more fuel. It is no good being upset or afraid of them. Just don't pay attention to them. Try and be cheerful.
The simple fact is that it is impossible for two thoughts to be in the mind at one and the same time. It is therefore an easy matter to rid yourself of bad thoughts by being quite passive. Simply don't think them. Think something else instead-think about Torah of devotion to G-d, or even about your work, and so on.
A person's thoughts are in his power completely. He can turn them in whatever direction he wants.
You must be very careful about what you think: a thought can literally take on a life of it's own.
...thoughts have great power.
Guard your thoughts carefully can literally create a living thing.
I have a question. Or three.
10 months ago