I love the message here. The human mind is indeed a complicated thing. The think though it that as complicated as it is, it can also be very simple. You are very correct in your saying that our emotions are our own responsibility and that by changing your beliefs and perspective, you can change your own life and how you relate to yourself, other people and the world in general.

The simple fact is that your emotional state in at any given moment is greatly influenced and indeed controlled by what you are focused on. As Tony Robbins says, where focus goes energy flows. If you are focused on negative thoughts, your emotion energy will flow toward a negative state. You can only be depressed by focusing on the negative thoughts, and similarly you can only feel happy or exited if you focus on thoughts and things that you associate with happiness or that you are exited about.

The truth of how the mind works can be simple at times. When someone says or does something to you, you will have certain thought, and the meaning you attach to these thoughts come from the beliefs you have about yourself, other people and how the world is or works. The meaning you derive from your thoughts and beliefs will dictate where you point your focus, and where you point that focus determines what emotional state will result.

You can choose to focus else where, which means you control what you feel. You can choose what things mean to you which means you can choose where your focus goes. You can choose to replace some of the beliefs you have that are no longer working for you but against you, and by changing your beliefs, you have just changed your life.