Bad beliefs and bad thinking cause practically all the trouble there is. Worry, mental argument, fretting, guilt thoughts, defeatism, all of these have a terrible effect on our morale, our happiness, and our ability to live constructively and fruitfully. But why do we carry on with them? It's partly habit, but it's also partly the 'hidden hook'. Every defect has a hidden hook: a covert justification, which is the reason why we're engaging in it. Someone who is trying to give up worrying may struggle to do so wholeheartedly, because of underlying false beliefs, which are the hooks attaching them to the worry, for example:
'Worry gives me the illusion of control and therefore safety.'
'If I stopped being a fretting failure, I would cease to exist.'
'I worry because I care. If I don't worry, it means I don't care.'
Exercise: For one day, every time you realise you're engaged in negative thinking (worry, resentment, guilt, in all their forms), come back to the moment, and practise an affirmation ('God has already solved all my problems') or practise a mental exercise (e.g. mentally extending quietness, peace of mind, and gentleness to everyone alike, knowing I will receive these back in the giving), but watch out for how the ego tries to pull you back. What excuses or reasons does it suggest for holding onto the worry, the resentment, and the guilt, in all their forms?
Write these down and discuss with someone else until you can see through them.
In Step Six, we come to be willing to have God remove all our defects of character, because we find them objectionable. That means we have to find them wholly objectionable: whilst we still perceive them to be affording some benefit, we will not let them go (NB they never defended or protected us: we only thought they did).
Once we can remove these hidden hooks, we can look a defect like worry in the face and be wholly committed to its removal by substituting faith, loving thoughts, and constructive action.