the sum of our internal world

Its fair to say that at a certain age we all develop the ability to direct our thoughts. Just as an example, pick the dish you ate yesterday and think about what ingedrients go in there.

Now you might be aware of the idea "you are the sum of the 5 people you spend most time with". Basically saying, you are the average of what you surround yourself with.

I think this also applies for our internal world as much as our external world. So, if we have the ability to steer (to a certain degree) our thoughts and we realize that our mindset it formed by the most common thoughts and ideas we think of.....why not decide which ideas and thoughts to entertain?