Challenging the negative thoughts can be very powerful. Especially when the negative thoughts originate from other people.
My first T suggested looking in a mirror and challenging negative thoughts that originated from an abusive relationship. I would be looking at myself telling the thoughts to shut up. I am capable, that's why people ask me for help, etc. I was essentially standing up to the part of me that believed my abuser was right and proving the negative belief to be untrue. The really hard part was apologizing to myself for believing the negative thoughts and forgiving myself for that mistake. Saying it out loud to the bathroom mirror may have seemed over the top at first, but it was empowering to take back mental control.