Many of the problematic behaviors that bring people to treatment - substance abuse, eating disorders, self-injury, avoidance, etc - have evolved as attempts to control unwanted thoughts or feelings. In fact control is among the most popular coping strategies around.
One of the main reasons we try to control our thoughts and feelings is because taking control actually works for us in some situations. Indeed, getting rid of things you don't like in the outside work is often both possible and effective. For example, if you don't like the color of your walls, you can paint them, and if you don't like your job, you can look for a new one. Unfortunately, what works well in the external world just doesn't work well in our internal world of thoughts and feelings.
Have you ever tried not to think about something? For example, if I tell you not to think about pink elephants, what happens? Probably you thought about pink elephants (which you have most likely not thought about the rest of the day or week). Because of the way our brains work, trying not to think about something causes that thought to stay in our heads - after all, you can't recognize whether or not you're thinking about something without...thinking about it! Therefore, trying to control your thoughts tends to increase rather than decrease the thoughts you don't want.
Similarly, you can't talk yourself out of emotions you don't want. Although society often tells us that it's important to control our emotions, it just doesn't work. Have you ever been told "stop crying" or "don't be afraid?" Did you feel differently after hearing those words? Probably not. We can't just turn off our emotions, and even if we manage to suppress them for awhile, the "rebound," and come back even more intensely than before. The reason we can't talk ourselves out of emotions is that emotions are regulated by the oldest part of the brain, that evolved before humans developed language. This part of the brain is pretty similar to the brains of animals like snakes and crocodiles. Have you ever tried to argue with a crocodile?
Unless you want to be eaten, you shouldn't argue with crocodiles. Nor should you argue with your emotions. In spite of cultural messages that it's important to control your emotions, and you'll be better off the more control you have, attempts at control really just make our difficult life situations worse. It's like trying to dig your way out of a hole you've fallen in. You might dig and dig and dig, only to realize that you're even deeper in the hole than you were to begin with. You might then decide to dig harder, only to get the same bad result. To avoid getting any deeper, you have to stop all the digging!
Emotions like sadness, anger, and fear are normal reactions to difficult situations. The only thing we should - or even can - do about them is experience them. In fact, we know that animals like crocodiles can learn from direct experience, and the animal part of our own brains can, too. So take the leap of willingness to experience the thoughts and feelings that you'd rather not have. Observe them, watch them come and go, and learn how both feelings and thoughts pass with time. We may not rid ourselves of pain that way - but avoidance wasn't really ridding us of pain anyway! However, we might be able to live richer, more authentic and satisfying lives - we just have to stop digging and arguing with the crocodiles!