MIND NEEDS INPUTS- GOOD OR BAD CONTINUOUSLY. 
The mind likes to take in information every time, like our body needs food. When we eat a balanced diet, our body is fit. Likewise, good information is an input that keeps the mind free from bad stuff. 
From early stages, we get instruction from parents, teachers, and seniors, and by and large, we obey them. Thus, the frame of mind is already well structured before we face the real challenges of life. 
Our formative stage is a crucial phase. Afterwards, we take steps to brush out bad habits and emotions and do everything to inculcate something good bit by bit. 
What we read, to whom we listen, and who is in our company make a lot of sense. It is therefore essential to make the right selection. Being bad-tempered is easy, while being a sensible individual is a tough task. It is a common observation. 
Once we allow our mind to process all information, we are most likely gathering crude input, which is likely to give substandard output. Feeding the mind with correct information is more important than choosing the right food. Because something wrong enters our minds, it is transferred to our belief systems. It is a frame for our thinking and emotions. 
When any belief is settled in our mind, it becomes our value. Now, it becomes very difficult to erase even a fraction of deeply rooted values. Cross-checking what we know from any sources, particularly at early stages in our lives, deserves our full attention for living a reasonable life.