When I was young I was quite negative. I always thought the worst and I never tempted fate. I got into the mindset that if I predicted that the worst was going to happen, then I would be pleasantly surprised if things went well or not disappointed when they didn't. But when you're young, you don't know yourself or your strengths and weaknesses and you doubt so much.
Years later I realised what a pathetic waste of energy this kind of mindset was. Very often if you think the best will happen it will. But negativity breeds negativity. If you think the worst will happen, it probably will.
Now that I am older, wiser and self assured I know what my strengths are. I have learned to accept compliments and I know that having a positive attitude and coming across as confident and strong is inspiring to those around you. If you tell everyone you're no good at something, that you're bad looking or fat or 'can't do' they will believe it and so eventually will you, no matter how untrue it may be. And re-enforcing the negativity to get people to pay you compliments will eventually lose you friends because they will get sick of always bolstering you and telling you the opposite of what you keep on saying.
I have in recent months come across several people who perpetually encourage this negative mind set and I really haven't got time for it any more because it's pointless and just plain annoying and I don't want to surround myself with it. It's always thin girls complaining how fat they are and fishing for compliments and negative whingers who really haven't got anything to complain about in life who wonder why their friends drift away and why they are left alone. Worse still are the ones who get slated behind their friends backs because of their negative attitude.
There's nothing wrong with being a positive person. People prefer it, those who don't probably wish they were like you and had your confidence. The more positively you think, the more people will believe in you.
If you have negativity issues, get help. It's not right and it's not healthy and it's very damaging to your relationships. No one likes a know it all or a self congratulatory snob, but if you are a confident and happy person you will attract the right sort of people and eventually become that happier person.