> Comfortable in this context means they no longer have any concern about their own job performance, knowing they have a "sure thing" and underperform in their duties.
There might be multiple things going on here though. While I'm sure there are people who will settle into a job and underperform because they are virtually guaranteed their position, I'm guessing there are a lot more people in a situation where compensation isn't even matching inflation/CoL. In the latter situation the employee may just not care since the company doesn't care enough to compensate them 'fairly'. Depending on a lot of factors it may be difficult for them to find a new job somewhere else, so outwardly it might look like they're just 'comfortable' and underperforming.
There might be multiple things going on here though. While I'm sure there are people who will settle into a job and underperform because they are virtually guaranteed their position, I'm guessing there are a lot more people in a situation where compensation isn't even matching inflation/CoL. In the latter situation the employee may just not care since the company doesn't care enough to compensate them 'fairly'. Depending on a lot of factors it may be difficult for them to find a new job somewhere else, so outwardly it might look like they're just 'comfortable' and underperforming.