It was a natural thing that he wasn't as formal as other ponies are with Princess Celestia. With the given circumstances, it was because of her and someone that was very close to him that he got his cutie mark. Two plain old gears, but they meant more to him with every job that he did. It all started when Charcoal was younger. He had a friend named cinnamon. She loved to bake and always put a hint of; you guessed it, cinnamon in everything that she made. Her cocoa fur and cream white hair made her pass off as more of a chocolate fanatic, but the obvious bag of brown sugar as a cutie mark said otherwise. She was the only one that knew of his... handicap. Charcoal never knew how to fully control his magic as a unicorn. He'd hide it from others and avoided any form of activities that required it.
It was then that she had an idea. She had a large assortment of recipe books and how-to books in her home. She grabbed this one book that she rarely read that dealt with machinery. She had lots of ovens, and other machines that were needed for her to cook, so it was no wonder that she had at least one book about stuff like this. Cinnamon showed it to Charcoal, and he began reading up on how machines work, and what to do in case of a breakdown. Since that day, he picked up more books on the subject and became more fascinated, moving along to even building things from scratch. However... his disability with magic came to light during class one day.
Cinnamon was with Charcoal when he was building a small cart that relied on shifting gears instead of the much relied electricity. She was ecstatic that he had found his "calling", but the other unicorns surrounded him with curiosity and scorn. "It'd be a lot easier to work on this with magic" they said "With magic, you don't have to work with your hooves". They kept pestering him over and over to use magic, and Cinnamon began to get worried. It all started to get to him: his anxiety, his nervousness, all this pressure suddenly taking over and he forced himself to use magic. That's when it all started to spiral out of control.
Charcoal tried using his magic to start up the cart by spinning one of the small gears. Little did he know, he forgot to tighten the screw that kept it in place. The gear wobbled and shot out from the cart, aiming directly at Cinnamon. He tried to warn her, but it was one second too late. The gear hit her in the head and she fell to the floor with a thud. Everyone, at that moment, the only moment where Charcoal needed someone to say something, anything, was quiet. Blood seeped in between the tiles on the floor, and he began to panic a bit. He tried to help her, everyone else just stood there, looking at him with such disappointment.