Our state of mind is essential. It creates the filter in which we see the world. How we see the world reflects in our actions and in turn effects our outcomes.
It's easy to fall into a negative state for a moment, a day, a week or longer, we would justify it with many reasons. The truth is being in a negative state affects your body physically and does nobody any good. No matter how extreme into any negative state you get into, it will not help or resolve any situation. It's not a matter of never getting into a negative state, that would be a daunting and impossible task.
What is possible is to realize when you are in a negative state that you don't want to be in, examples are feeling, sad, mad, angry, frustrated, anxious, or depressed. When taking notice consciencely you can then snap out of it. Snapping out of it can be done in many ways that are different specific action but generally the same to each person. Strong effective tools are changing your physical state to a strong one, pick up your shoulders, raise your chest, lift your chin and take a deep a deep slow breath. Follow this with an immediate shift in focus to anything other than what stemmed the negative state, try something that brings a smile to your face. The last major tool is to change the language and replace limiting negative harsh words with kind optimistic and fun words.
The more this is practiced the easier it is to stay consistently in a positive state or to more quickly snap out of a bad one. Things to remember when your feeling great is what caused this feeling so that you can recall this in your mind in times of need. Use your senses to elevate your mood. Listen to some feel good music, look up some great vacation spots, call a loved one or a friend, take a spa day there are many tools to fill your chest with.
Staying in generally in a positive state does wonders. It helps attract positive people and energies or can give light to those in the dark. It helps see the world thru a better filter. It allows you to go thru the days that may not be good but still see the good in everyday.