If you have been brought up in a happy and positive atmosphere, there is more probability that it will be easier for you to think positively. However, If you have been brought up under poor or difficult situations, you will more probably be more inclined to negative thinking.
We view the world through our predominant mental attitude. If our thoughts are positive, that is fine, but if they are negative, our life and circumstances would probably mirror these thoughts.
If you believe that you are going to fail, you will unconsciously sabotage every opportunity to succeed. If you are afraid of meeting new people or having close relationships, you will do everything to avoid people and relationships, and then complain that you are lonely and nobody loves you.