It is indeed true that what you believe and think even if not consciously but it exists in the back of your mind maybe through what you heard or what you saw around you can make prominent changes in your actions and results too.

Therefore it is advisable to surround yourself with people and things who revert you towards optimism and positivity.

When you think in the right direction, you tend to do the right or desirable actions and work towards your aim finally leading to the accomplishment of your goals.

So it is rightly said, "Surround yourself with things and people which lead you towards your objective and helps you to become a better person."