Your negative thoughts become distractions forcing you to pay attention to, and do things that really don't help you achieve the success you want. This applies for any areas of your life.
Negative thinking can sneak up on you and in most cases, you won't even realize that they're filling your mind and turning into beliefs slowly destroying your hopes, desires and dreams.
Everyone has to deal with them every day. Positively remind yourself, you have to live the life you want to live.