- His level of "careful" didn't keep up with the high speed of his work;
- He could not seem to make himself stick to a scripted procedure if he "knew" the steps, and this included source control steps (!!);
- When he got bored, which was frequently, instead of applying himself to learning new things useful to the team, he turned to his phone and texted/facebooked/etc., leaving the image of someone not doing their job.
It didn't help matters that he never listened to anyone, and had an argument and an excuse for every single thing he did -- some bordering on the ludicrous.
He did not hold the record for fastest-fired employee, but he ranked high on that list.