Even positive people often doubt and despair. You don’t need to rip yourself off of everything that makes you human just so you can be positive, grateful or optimistic. We all come in a package of strengths and weaknesses, and in the journey of self development it is of crucial importance that you embrace (only acceptance is not enough)yourself with them all. Anxiety and worry does not make us less optimistic. If any it only makes us human.
So yes, positive people have negative thoughts too.They just dont let those thoughts dictate their actions. They know better to realise that they might not have control on the thoughts but most definitely they can silence them with actions.
Only when you truly start living by this verse do you realise how true it is. It has the power to reshape your entire existance and get you out of whatever it is that is paralysing you. Sure it wont happen overnight but as I always say, one of those days when you aren’t paying attention it will.