Every single moment you are bombarded with thousands of sensations from outside. Our five senses gather information from surroundings and process them in our brain to experiences. These experiences are then coloured with our feelings according to our past impressions and the resulting conclusions are stored in our subconscious. This process is repeated thousands of times in a single day of an individual.
The patterns stored in your subconscious during the past determine whether your life is happy or miserable, most of the time. If what you have accumulated in the past mostly is painful impressions, any outer information entering you will be processed accordingly and given the colour of an unpleasant experience. Similarly, if you have stored most of the impressions as pleasant, outer stimuli will again help you form a pleasant impression inside. This is a chain reaction which moulds your outlook of life and personality.
So, what can you do to make yourself healthy and happy? Every moment you should be fully alert. This is not a simple task as it sounds. Even though it requires a long time to practice, you can pick and choose the content and the information you take in. Select only good stimuli from your environment, as far as possible. Let your eyes behold the beauty of nature, your ears listen to harmonious music, your nose never miss the opportunity to smell the fragrance of a flower, the tongue taste healthy, sweet taste of natural fruits and vegetables, and your feet touch soft, wet grass in the morning time. The pattern of subconscious impressions can make or mar our whole lives.
So, what we can do is to select pleasant experiences as far as possible, and even when you encounter any unpleasant sensation or experience, consciously process the same into a pleasant one through developing an optimistic attitude.
Even all the above sounds quite simple and straightforward, remember, most of us are slaves of our habits. We react to outwards stimuli automatically based on our habitual thinking. Only arduous work can help you overcome them and mould your personality to higher standards.