It's not just a blood group; it's a motto to live by. The world is comprised of two kinds of people: they who see the glass half-empty, and they who see it half-full. If you constantly give negative feedback to the mind, it will become negative. If you tell yourself that life is tough and that you will never succeed, you will fulfill your own prophecy and you will never succeed. If you choose to think encouraging thoughts and believe that with God's grace and self-effort you will succeed, then you will. Give the mind positive reinforcement and make it your best friend.
Research shows that if you tell a child again and again that he is stupid, he will invariably become stupid. If you tell him that he is intelligent, he will behave intelligently. The teachers we remember the most are the ones who offered us encouragement and hope. My ESL teacher in high school encouraged me to study French and German though I was still learning English. Through her I discovered my deep interest in languages that has stayed with me to this day.
Be positive. You will not only help yourself but everyone who comes into contact with you.