I recently wrote about a phrase you should never say if you want to be successful in your career. That phrase is “I can’t.” There are few things more annoying for an employer or potential employer to hear than that you “can’t” do something. As my friend’s mom says, “Can’t means don’t want to.” Wise woman, that one.

Now I’ve got another phrase to add to your must ban list, one that might even be more nefarious than “I can’t.”

That’s not my job.

Along with “That’s not my job” also ban its close cousins, “There are people for that” and “Someone else will do it.”

These phrases usually mean something like “That’s beneath me,” and “I’m too busy.”

Nothing should be beneath you. And you’re not too busy. Have you ever noticed how the people who say they’re the most busy never are? For ten years I’ve been writing a health column for a magazine, for which I have to interview an average of five people each time I publish it. Over the years I’ve come to realize that it’s always those who are busiest and most in demand – say, who have just flown in from an overseas conference and have to perform surgery in an hour – who are the most generous with their time and insight, and who are always most willing to spare a few minutes right then and there.

I once worked with a boss I liked a lot. But one thing that drove me crazy was her refusal to let me do things that were outside of my job description. So, I would be waiting for images to publish with a story, because the art department was backed up. “Can’t we just get them from the image provider and crop them ourselves?” I asked a few times.

“No,” she would reply. “That’s not your job. There are people for that.” And so I would wait, sometimes until the next day, for the images I needed, even though I could have gotten them myself in 15 minutes. It was a frustrating and my time was not as well spent as it could have been.

I understand that there are situations in which you do things that aren’t your job at your own peril, like some union situations. For example, a friend who was working at a major US concert hall once moved the piano bench a few inches and got yelled at and sanctioned because moving the piano bench was someone else in the union’s job. He thought they were joking. But they weren’t. But in most cases you’re not going to get in trouble for not asking someone to do something for you.

A far more effective plan is to assume everything is your job.

That’s not to say that you should go around undercutting other people, doing their jobs and becoming a control freak. It’s to say that you shouldn’t refuse a responsibility that you are capable of taking on based on the misguided notion that the responsibility is not yours.

In 2009, I read an interview with Applied Materials CEO Mike Splinter, and something he said stuck with me. He said:

“Before I joined Applied Materials, I worked at Intel for two decades. I recall a session with Andy Grove. It was 1984 … In his talk Grove advised us to always assume it’s your responsibility. By that he meant to take on a job, even if it wasn’t yours. That’s a general thought, but it creates specific action and works across almost any situation, from picking up garbage on the floor to a new product idea.

“If you automatically assume it’s your responsibility and do something about it, that makes the company better. Those who can recognize that are the ones who end up being more successful.”

Those who can recognize that and act accordingly in their day-to-day lives are also the people who make the world a better place. The people who take care of society’s underdogs, or simply pick up litter that someone else dropped. We would all function a lot less effectively without them to pick up the slack.

We should all be doing our best to be like those people.

At work, your job is to contribute to making the organization for which you work successful in whatever way you can. To that end, it’s all your job.