Asimov tells a story in his autobiography of having trouble in an English Literature class in college. Being usually a straight-A student, he arranged a meeting with the professor to discuss his difficulty in the class. The professor was less than helpful, stating, "You know what your problem is, Mr. Asimov? You just can't write!" At which point, Asimov pulled out the check he had just received that day for one of his short stories from his pocket and waved it in his face, saying, "I got this for my writing." And walked out.
Awesome, indeed; however, the above combines two separate incidents. When the professor told Isaac he "couldn't write," Asimov's reply was, "I'll thank you to not repeat that slander to my publishers." The incident with the check occurred when a customer in the Asimov family candy store took umbrage at Isaac's failure to say "Thank you" at the close of a transaction. "My son," said the customer, "made fifty dollars this week though hard work. What do you do to earn a living besides standing here?" "I write," answered Asimov, "and I got this for a story today," and he held up the check (for about $64, I think).