I am sure we've all heard this before, but it's good to be reminded from time to time to protect your thoughts.
Biblical:
Proverbs
23:7. For as he thinketh in his heart, so is he: Eat and drink, saith he to thee; but his heart is not with thee.
Phillipians
4:8. Finally, brothers and sisters, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things.
Scientific:
We think via neurons. The more we dwell on specific thoughts, the more brunched up neurons become inline with whatever we are thinking about. Remember, neurons only carry electrical signals (information), the type of information doesn't matter. If all you think about are negative, non-constructive things, your mind will access those sorts of thoughts quicker (you are practicing negative thought patterns and your mind becomes better at whatever you dwell on), and your subconscious will be programmed to see negative even when you aren't actively thinking about it.
Your thoughts end up shaping you as a person because they wire your mind to think in the way you've decided.
Be careful what you think about and also be careful about what you watch as well.

Biblical:
Proverbs
23:7. For as he thinketh in his heart, so is he: Eat and drink, saith he to thee; but his heart is not with thee.
Phillipians
4:8. Finally, brothers and sisters, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things.
Scientific:
We think via neurons. The more we dwell on specific thoughts, the more brunched up neurons become inline with whatever we are thinking about. Remember, neurons only carry electrical signals (information), the type of information doesn't matter. If all you think about are negative, non-constructive things, your mind will access those sorts of thoughts quicker (you are practicing negative thought patterns and your mind becomes better at whatever you dwell on), and your subconscious will be programmed to see negative even when you aren't actively thinking about it.
Your thoughts end up shaping you as a person because they wire your mind to think in the way you've decided.
Be careful what you think about and also be careful about what you watch as well.
