"You know the truth by the way it feels". How many times have you been advised to pay attention to and respect your intuition? Probably a lot. This is a great way to monitor how a person or thing always causes you to feel. If those feelings are negative, heavy, and down trodden, then whatever made you feel this way is impeding upon your peace.
How Does it Make You Think?
What thoughts run through your mind when in the presence of this person or thing or place? If you constantly trail off into negativity, pain, and disharmony, then seriously question what about this thing or person or place is causing you to think this way. Then decide if and how much you should separate yourself from it.
This one is probably a lot easier to decipher. When in a place, or around a person, thing, or people, how does your behavior differ? Surely, we may need to alter our behavior depending on a situation. For instance, changing your vocal tone in a library, being gentle around a baby, or handling items carefully in an expensive china shop. However, if your behavior changes your morals, pushes you into destructive actions, and alters your being for the worse, then you are experiencing something that is a threat to your peace.
Understand that you are ultimately the only one who knows what conditions are peaceful for you. Therefore, always check in with yourself, and take time to know who you truly are. What are you aiming to protect your peace from?