Thoughts are something very introspective and diverse to so many different people because there are infinite number of possible thoughts going through the collective population's minds. Thoughts are also polar, meaning there are positive thoughts and negative thoughts.
The problem is, the thoughts themselves are not intrinsically positive or negative. It is us that define what positive and negative is and so we often get caught up in whether or not it is acceptable to think in a certain way or is there a particular way to think, the "right" way? the truth is there is no particular "way".
What this means in terms of thoughts is that, there are no positive thoughts or negative thoughts, they are simply just thoughts. A byproduct of the physical mind(brain). You can either choose to accept or reject those thoughts. When we do this, it is important for us to not be identified with our thoughts because you are not the thought itself but the awareness of that thought. The reason i say this is because thoughts are always all over the place; we can never control the thoughts we think, is it possible to not be in control of something that is supposed to be you?
So right there, you can see the separation between what You Are and what Thoughts are.
Although what Buddha said is true; "what we think, we become" but we must put that into context first. The reason we become what we think is because we are identified with thoughts but really we can choose to become anything we want, it does not have to depend on what we think we should be.
We have the belief that thoughts have patented ownership "these are my thoughts", "these are your thoughts". This is completely devastating to your personal well-being.
This is because Thoughts are also very closely related to emotion. When a thought arises, you experience a relative emotion to that particular thought. Sometimes that particular thought makes you angry, sad, happy, etc. and so thoughts heavily affect your emotional well-being, especially when you are identified with thoughts. At the same time, experiencing an emotion due to an external situation can affect the way you think. So it is a two-way relationship between thought and emotion.
When you are identified with what you think, you will act interms of what you think is you. So you are left with not being your trueself but simply being what you think you should be. There is an identity crisis. Who am I? *soft whisper* you are not your thoughts.
