Few people in the workplace are craftier than a slacker.

After all, nobody likes the kind of person who leaves all their work for somebody else to do. It takes practice, skill, and a somewhat ironic amount of effort to avoid doing your job in a way that is successful and does not eventually lead to conflict. There has to be a plan in place that nobody would suspect.

However, it is fair to say that the kind of employees who prefer to slack off usually do not work hard enough to make their strategies foolproof. Unless they work a job that is genuinely low effort, somebody is going to notice at some point that their workload is increasing, and they are going to try to find out why that is. 

It can be deeply frustrating and disappointing to realize that a colleague is not doing their job, but what can be even more awkward is the attempt to rectify that situation. They aren’t likely to be the kind of individual who deals well with confrontation, and there is every chance that a manager has reasons for taking their side.