Have you ever considered your thinking style? Do you tend to view things as if you have "gloomy specs" on? Always seeing the negative in things? When faced with a stressful situation, or you experience anxiety before a performance, do you perceive this as a threat, or as a challenge?
Essentially, the way we interpret events and situations around us influences our emotions and in turn influences our behaviour. If I interpret say a steep hill which I want to cycle up as a threat then I'm going to be anxious going out there, maybe making me doubt myself that I can cycle up it, which will have a knock on effect on my confidence and I'm likely to find my performance suffers as a result. If I had interpreted the same hill as a challenge then I am approaching it more confidently from the outset, as this is something I want to conquer and I am more likely to believe that I can do so and, therefore, perform better when I am cycling up it, i.e. not listening to the screaming in my legs or lungs, but instead seeing that as part of the challenge and committing to keeping on going. If you interpret that hill as too hard for you, even before you have tried, then you're not going to try it, you will avoid it, meaning that you might have to cycle the long way around routes, rather than going up it as your cycle pals do.
If you tell yourself that something is too hard then you're likely to believe yourself and as such you might feel down or anxious when thinking about that event, that you're not good enough, that you can't cope. We all respond to the same situations and events differently, meaning we interpret them based on our past experiences and beliefs, and we experience different emotions as a result of these interpretations and therefore our behaviour might be different. Ask yourself how your thinking affects your day-to-day life, your training, your work, your performance in various arenas...is there room for improvement? Just because you have always thought that way doesn't mean that you can't change it if you recognise that's what you want to do and commit to doing so.
Don't let your negative thoughts control what you do and don't do. Don't let your thoughts make you miss out on opportunities or ruin situations. You can regain control. You can focus your attention on what you choose, you just have to learn to recognise where you focus is and then re-direct it to where you want it to be from now on.