“Man often becomes what he believes himself to be. If I keep on saying to myself that I cannot do a certain thing, it is possible that I may end by really becoming incapable of doing it. On the contrary, if I have the belief that I can do it, I shall surely acquire the capacity to do it even if I may not have it at the beginning.”
― Mahatma Gandhi, founding father of modern India
It is true that if you want to achieve great things, you have to believe you can do it first.
Next, try to acquire the capabilities of doing it. Either through learning or external help.