Overthinking is a kind of addiction to which each and every person is addicted to at some or the other point. So, overthinking is very common and may be caused by self-doubt and self-esteem issues. No one ever know how much time they spend in thinking. Some people are there who overthink even a little dove, until it becomes large and more horrendous than it is. They overthink positive things, so much that it does not look positive anymore (and here the anxiety starts to build) and just because of this, the happiness which is coming to them from that moment vanishes.
Thinking is a great thing which is done by each and every person, but overthinking is not a great thing at all. If overthinking is done one to two times then it's Okay, but overthinking every time leads to misery and anxiety. When you know you can't change the past, and future haven't arrived yet so there is nothing you can do by overthinking and the only time you can do anything is "Now." This way you stop worrying with things that are out of your control (which is a great nonsense and a good waste of time if you think about them.) Start caring about your present, and that's only time you are really living on! Of course you can learn from your "Past," and as well plan your "Future," but in the end "Now" is the only thing which you have. So, "Stop overthinking, and live in your present!".
Living in the present means letting go of the past and not waiting for the future. It means living your life consciously, well aware that each moment you breathe is a gift. Overthinking takes you to your past mentally and then do not let you think about your present. And once you have reached to your past mentally, the happiness which is in the present isn't able to reach you. It will tease you more and more as you think about it. So guys, stop overthinking about your past, because it will give you pain, tension and stress more than happiness. Start living in your present because our present is really beautiful. Smile every day and it will make your day joyful. And one more thing "The happiness and joy you are getting in your present, aren't available in your past!" So start living in your present and do not overthink.