It's because I'm so humble, obviously.
You know how difficult it is to put in eight concentrated hours in one day. You've probably had the experience of being burned out one day from concentrating the day before or burned out one month from concentrating too hard the month before.
You've probably had days on which you've worked well from 8:00 am to 2:00 pm and then felt like quitting. You didn't quit, though; you pushed on from 2:00 pm to 5:00 pm and then spent the rest of the week fixing what you wrote from 2:00 to 5:00.
The people who are the worst at programming are the people who refuse to accept the fact that their brains aren't equal to the task. Their egos keep them from being great programmers. The more you learn to compensate for your small brain, the better a programmer you'll be.
The more humble you are, the faster you'll improve.