You can stop it from building a nest in your hair."
Everyone has thoughts that are positive and negative. Some thoughts will just not serve you if you let them run you. For example, worry, there is nothing about worry that will serve you. You can do something about a situation that is troublesome but sitting and worrying about it won't do a thing for you or anyone else.
Some thoughts might make you angry if you stop to think about it. So why spend your time in upset? If there is something you can do to make changes to your life for the better, that is great. Going over and over something that is negative will only distract you from the positive that can comfort, build or nourish you.
If you spend time thinking about something your friend/family/coworker did that hurt you how will that serve you? Need to set boundaries? OK, so set them! If it's a pretty much regular relationship, you have a choice to look at the dark side of that person or pick a new thought that will change your own chemistry for the better.
If something pops into your mind that does not serve you, shoo it away!
Love and blessings,