We learn through our senses. We take in information via our senses and then our minds compute that information and make sense of it all. We are, all of us, inherently "suggestible". We learn through mimicking, copying and suggestion. Things seem to "rub off" onto us.
The ability we human beings have to learn in this way is amazing; it is fantastic...so long as we are mimicking, copying and responding to the right suggestions. If we hear something a few times, whether we like it or not, we will tend to find ourselves repeating it; hence sometimes hearing an "annoying" tune in your head. If we do something several times we tend to keep doing that thing, whether we really consciously want to or not; it becomes a habit, smoking, for example, or buying a snickers bar every time you fill up with gas.
Our minds work by generalizing patterns of thought and behavior over context. For example, as a child you learned to recognize a glass as a glass. And then every time you see any type of glass it is recognizable to you as a glass - it has been generalized in your mind over context. Where the generalization is accurate, this ability we have is supremely beneficial; when it is flawed, it can have an extremely debilitating effect...
How many times have you heard yourself say "I can't putt", "I can't get off the tee", or some variation of this theme? Is this generalization accurate? The reality of the situation is that on this particular putt, or this particular tee shot, you used your club to hit the ball and the ball went wherever it went. Full stop! That is what happened; nothing more, nothing less. Why should that mean that you CANT putt (ever) or get off the tee (ever)?
The problem here is that you aren't looking at the reality of the situation, you aren't focusing on the present, you have switched your awareness into a "generalization" mode, and you are creating a self-fulfilling prophesy. You end up not being able to putt or get off the tee because this is what you have suggested to yourself. In the words of Henry Ford "If you think you can you can; and if you think you can't you're right".
If someone else was as critical about your golf as you are, how would you react? If your "mates" stood there saying "you can't putt" would you just stand by and take it? Or would you get a bit defensive and feel that the comment was "unfair" or "unnecessary" to say the very least? It pays to remember that we humans respond to suggestions, be it consciously or subconsciously, and that we can choose to accept or to reject those suggestions.
Would you be as critical about your playing partner's swing as you are about your own? Why be so hard on yourself? Why be so very negative and destructive? Why do you actually consciously choose to do something which will destroy your golf game? You know that you are telling yourself you can't do it, so why not change the language you use?