You choose to believe. You've done it before. Do it where it really counts. Believing in yourself is a choice. One that you need to make. If you really want to know how to believe in yourself watch the video on my YouTube channel: https://youtu.be/RWMsN_atMhg
Whether you think it is impossible or possible you are right. If you want to shield something find a way not an excuse. What have you considered impossible in the past but would like to achieve in the future (now that you know better)?