Why do you want to monitor your feelings and adjust your thoughts to feel good on purpose?
Because that is what you are here for. (Actually you are here for the purpose of expansion --the inevitable result of your focus on desires -- and for joy--- the result of allowing the solution)
Every consciousness, from a single-celled amoeba to a plant to a human, encounters conditions which inspire a desire for improvement. That observance of something unwanted (called 'contrast') creates the equal and opposite solution to the problem. (There is far more to be said about how that works, but for the purpose of simplicity we'll leave it at that for now).
What you think about is what you get. What you believe is proven to you again and again.
Common disincentives to stop focusing on negative thoughts (which upon release would thereby allow positive thoughts):
(Sheesh: that sounds like a triple negative statement! In other words: Why do you keep worrying?)
1.) The negative circumstance is so compelling! It is right there. It's 'real.' You can see it and smell it and touch it... People are talking about it.
2.) Law of Attraction is bringing you thoughts and more circumstances that match the tactile reality of the unwanted situation.
3.) Everyone in your life has taught you to confront problems. Solve them. Tackle them. Overcome them. Fight against them. Avoid them. Judge yourself by them.
4.) There is excitement in fighting a problem. (a false sense of temporary power over circumstances)
Sometimes also known as: drama
5.) The lure of being 'right' is more compelling than letting it go. (lots more about that later)
6.) You don't know you can stop.
7.) You don't know you must do so if you want the joyful life you came for.
Why should I focus my thoughts to feel good?
1.) Because it feels good.
2.) Because it is who you really are. (Free and loving an creative and excited and inspiring and inspired...., as opposed to worried and fearful and guarded and critical...)
3.) Because you will receive the solutions to each and every problem.
4.) Because you will live the unlimited, expansive life you came to lead and experience, exponentially, more improvements for yourself and everyone you encounter.
5.) Because you will inspire others by your example.
6.) Because you will uplift others by your mere presence.
7.) Because it hurts not to.