Like everyone has said, it's purely because you aren't your thoughts, in the same way that you aren't your feelings, your memories or your elbow. Your thoughts are just another part of you much like the rest of you, but it's the part that almost everyone thinks of as them because it's so prominient. It's the brain content that fills the gap inside of existing.
Much like your feelings or your unconsious reflexes, your thoughts are not controlled as much as they are observed. You as a being don't think, you observe your mind that thinks. You don't feel, but you observe feelings that arise from the body. If this is the view you work from, you can see that it's not a matter of trying to make yourself do something specific, but a matter of training a part of you to behave differently.
How do you train something? First, awareness. You need to know what it's doing before you can correct it. You need to hear your thoughts and not act on them. Listen to them as a seperate creation apart from you. Then you know what you have to deal with. Second, discipline. If there is an incorrect behaviour, stop the behaviour and reprimand your brain. Don't get angry at yourself, because it's not you that's thinking. And don't get angry at your brain, because it's just a tool. Just a simple message of "don't think that anymore" will suffice. You can also reward it with good messages when it delivers positive thoughts. Thirdly, education. Feed it information that will help it with it's job. Reading or listening to positive material in the style that you wish to follow is one of the best ways. Immerse your brain in the environment you wish to cultivate.
As odd as this whole lot sounds, it works. It also takes time, patience and practice. One cannot master anything overnight, it takes years, and this definately includes mastery of thought. I hope this explains not just why you can't but also how you can.  |