Our Rebbe said in a Sicha that if a Yid truly resolves to accomplish something that is out of the range of his G-d given talents and capabilities, then Hashem will open new channels of strength for him from above.
From this story we can see the difference between an accomplished Torah scholar like Reb Aisle who, even in his youth, was considered a genius and a Rebbe. Reb Aisel needed special powers to be opened for him by the Alter Rebbe in order to manifest mature intellect. While the Tzemach Tzedek was able to absorb and memorize that very difficult maamar as a 3-year-old.