Not My Job
When you're a workaholic, there comes a time when you have to say no to certain tasks. You can't allow yourself to be swallowed by the expectations of others, and there are appropriate times to resist additional responsibilities.
Others have a different issue. They see their job with tunnel vision and refuse to step outside the lines to help their fellow coworkers. It could be the result of laziness, but more likely it's because they don't truly care about their work.
People like this pawn off tasks not in their job description with a righteous, "how dare you ask me to do this?" But those invested in their work, who care about the quality of a product being delivered, do everything in their power to see it finished.
Certain things may not be in your job description, but the "job" goes much deeper than bullet points on paper. A company made up of individual silos can never achieve what teamwork is capable of, and sometimes teamwork requires you to step outside the lines.