“Every thought affects you. Gurudev Sivananda has written about this in his book Thought Power. A bad thought has three different effects. First of all, it negatively affects the subconscious mind of the person who sent the bad thought. Then it affects the person to whom it was directed. Thirdly, it joins with the other negative thoughts of other human beings and they are all in clouds, black clouds, on the same vibratory level. But if you have a pure mind, if your thought is good, if you repeat your mantra and practice your meditation, you develop psychic armor. Your thought will not tune to their thought, it bounces back.
You attract a thought of a particular nature because you have the same wavelength. Once your wavelength is very high, these negative thoughts will not join your thoughts. But if your vibrations are low, and you live amongst negative people whose vibrations are low, you will be affected by their thoughts. So, you can increase your thought level, that’s the only way you can help yourself. Just repeating a positive thought. “I am strong, I can help myself, I can bounce all these thoughts” is not going to help you.
Overreaction to words and jumping to conclusions are weakness of the mind. The vrittis, the thought waves, must be restrained, not only during meditation, but at all times. One must be particularly wary of praise, for this too is verbal delusion and the ego is ever ready to pounce on any opportunity to see itself as better or different from others. This is one of the most difficult problems for swamis and Yogis and spiritual people.
You have the infinite power in your mind; believe that. Use it; assert it. The infinite power is within you. Only when you understand that are you going to be a Yogi.”
Teachings on Yoga Life