This is a deceptively simple and maybe to some a bewildering quote from Seligman . Deceptively simple, you are what you are! Nevertheless, how long and how much energy have you spent looking, searching for an answer to this very simple question why? Bewildering because the quote implies that you can change and somehow this process is obvious. However, after years of trying to change those thoughts, put a lid on fear and hide feelings (even sometimes finding some relief), the old thinking, the old fears and those old emotions come flooding back again.
It does not have to continue this way. You don't need to put all your energy into this repeating cycle of chasing happiness by trying to remove your negative energy, thoughts and feeling.
You can choose a different trajectory for your life worth fighting for now and into the future. You can change the mix, that's how you can achieve new outcomes and write a new life history that is not bound up in the old struggle. You can get out from under your fears and anxieties, stop wrestling with your stresses, and stop putting all your energy into getting rid of anxiety and fear. You can refocus your energies and get your life back! Acceptance and Commitment Therapy (ACT) will show you how, if you are willing.
The ideas presented in ACT are "backed by a growing research base showing that anxiety management and control feeds anxiety and fear, shrinks lives and promotes suffering...Instead of teaching you a new way to control anxiety, we'll go to the root of the problem in a way that will increase your vitality and your ability"  to create and live your life worth fighting for now and into the future.
ACT offers strategies and skills you can use in your everyday to bring acceptance, compassion and gentleness to unpleasant thoughts, feeling and memories. A shifting perspective to help people change their relationship with their inner selves and learn how to live better with whatever they might be feeling and thinking.
ACT counselling is designed to help you get something different by doing something different.
Are you willing to take the first step? I invite you to contact me and take that first step to living your life worth fighting for.
 Seligman, M. (1993). What you can change and what you can't: The complete guide to successful self-improvement. New York, NY: Vintage Book.
 Forsyth, J. & Eifert, G. (2016). The mindfulness & acceptance workbook for anxiety. (2nd ed.). Oakland, CA: New Harbinger Publications, Inc.