One of my least favorite phrases to hear in the workplace is, "that's not my job." Many times it's an accurate statement, but said from a place of either resentment or fear.
If a person thinks they might be under fire, the "it's not my job" defense can deflect blame. Obviously you're not responsible for said task and by default cannot take the heat for a job done poorly. A form of self-preservation.
The more offensive form appears when a person is under the guise of "protecting their boundaries" but in reality lacks a sense teamwork. Yes, there comes a point when a workload too heavy can crush you, but more often than not a sense of comraderie will develop a healty team over a bunch of sandboxed employees.