A new life begins today!
Self-suggestion basically means placing a thought in your subconscious. Whether it is good or bad, this is a special problem. When you think, "I can do this," "I look good," "I'll be successful," "It'll work out," you'll believe these things, you'll insert them into your psyche, you'll act accordingly, and ... you'll attract the success you want, like a magnet.
On the other hand, everyone has negative thoughts. Usually, they are opinions "borrowed" from others. If a person with some kind of authority (boss, parent, friend) tells you something negative (you can't do it, you don't do well, etc.) there is a good chance that you will believe him and take over the idea in the long run. Thus, not that person, but you yourself subconsciously introduce the negative idea, which will bring with it other negative ideas, failures, attitudes of a defeated person.