In my previous article I cited a statement by Rav Simcha Zissel, who interpreted the verse in Tehillim (118:13), "Pushed, I was pushed to fall, but Hashem helped me", to mean that there is an internal force in a person that seeks to crush him by making him feel inferior and inadequate. This force is the yetzer hara. A person may seek psychological help to improve his self-esteem, but the psychologist cannot counter the power of the yetzer hara. I pointed out that only intense tefilla can be effective.
The feelings of inferiority and inadequacy are a delusion wrought by the yetzer hara to disable a person. The first line of defense is to refuse to accept the yetzer hara's ideas. This is extremely difficult. I suggest comparing in to the "phantom limb" phenomenon.
A person who has had a leg amputated may complain of pain in his non-existing toes. He can see that he has no leg, but still feels the toes. It is essentially a hallucination and delusion. Some medications and treatments may help. Eventually the phenomenon disappears. It is most difficult to accept that he has no foot, even though he sees it.
When the yetzer hara causes the delusion of inferiority, it is very difficult to deny its reality. It takes a great deal of emunah to do so. If a person has sincere trust in someone, he can accept that someone's opinion that his feelings of inferiority are delusional. The verse that R' Simcha Zissl cites is the answer, "VaHashem azarani" - Hashem continuously does many good things for us, e.g. give us life, health, family, a roof over our heads, a job, etc. He sees each of us as worth having around and supporting. Intense tefilla, in which we must ask Hashem to help us see ourselves in the positive light that He sees us, is necessary.
A person may also have feelings of low self-esteem which are due to circumstances such as deprivation of love and failures. These may be overcome with psychological help. I addressed these in my books Life's Too Short, and Ten Steps to Being Your Best.
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