This is true and you can actually make things which seem to be the impossible be possible. You hear a lot of people put them selfs down like "I can't do this" or "I am never going to get any traffic to my website". Truth is thinking like that honestly you wont because trust me I use to be the same . So lets start the next time you think like this change the negativity around "I can do this and I will do it" positive thinking can be a powerful thought in your mind.
Like they say " If you want something that bad don't and never give up" so turn your negatives into positive and give it a while you will see the difference in your life you will see the strides you have come and to where you are at now in your life. You herd the word Power of suggestion , it is powerful at that you could talk your self out of things easily by saying "can't do this can't do that" without even trying most of the time. Give it a chance and give your self a break.
Try making a list of things you are not good at and then from the top trying to do them one by one and keep telling your self YOU can do it. Since I was a child and maybe you agree here are parents would comment every time we said we cant do it or anything on those terms and they would say "There is no such thing as can't". So remember just try only a few or one at a time.
Lets say something simple like your favourite game you like playing which you never finished because you CAN'T do it . Tell your self you can and repeat in your mind you can. I know it sounds simple and silly be you be surprised lol. Now go back and try it . Maybe your saying You can't write quality content for a blog or posts/discussions now say you can and go back and try it this time take your time take deep breaths and relax and write. You see what I mean the simple things in life make notes and prove your self wrong . Yeah you may make mistakes at the beginning its the end result you need to get to