The statement, "the littlest things matter the most" has some truth to it. However, I don't think it should be your reasoning as to why you're getting worked up and stressed. In life, it is important that we are thankful for every experience we encounter. We tend to forget how grateful we are for everything until the holiday season is around the corner. The ultimate goal is to live life to its fullest and not let the smallest things bother us. Don't let one thing turn your good day into a bad day.
You should ask yourself this whenever you're in a bad mood, "Was it a bad day? Or was it a bad five minutes that you milked all day?" Sometimes we forget how little it takes for us to ruin our days, especially when we are overwhelmed. It is important that we don't stress the small stuff. You should also ask yourself, "Will this matter one week from now? A month from now? Or even a year from now?" If you stop, breathe, and take a few minutes to think about it, I guarantee you that the answer will always be no. No because whatever is bothering you right now will not matter in the long run and that it is not worth dwelling over.
If something has been making you unhappy for awhile now, the answer is right in front of your face. You should eliminate anything that is getting in the way of your happiness. If people are meant to stay in your life, they will. But if it's their time to leave, let them go. Life is too short to be negative all the time.
The only little things that should matter are things that lift our moods. For example, small gestures, hobbies, surrounding ourselves with good company, and doing something small every day for 15 minutes to better ourselves. These are the "effortless" actions that will help us grow. When you fully assess a situation and realize how small it is, let it go and move on with your life. Concentrate on things that are worth your time and effort. Don't look back and dwell on something. Remember, "You are your worst enemy." We are the one of the only people who can help "destroy" ourselves with the overthinking. Overthinking can kill us, meaning it will destroy our mental and emotional capabilities. You notice how much your mood changes when you're consistently stressing about something that's on your mind.
Positivity and looking on the bright side of things is how it should be. We should let things go and move on from situations once we believe we have handled it in the maturest way possible. After that, it is respectable to move on and have no hard feelings.