Parkinson’s Law almost certainly doesn’t apply to your people.

Parkinson’s Law is the notion that work expands to fill the time allocated for it. In other words, it’s the conviction that the only way to get work done is to set an impossibly optimistic delivery date.

An argument a manager may make is that there are workers who seems to be avoiding work, have no standard of quality, or can’t get the job done. However, these workers are not a result of Parkinson’s Law but rather one where a worker finds the work too difficult to do and needs to be reassigned. Pressuring a worker that is struggling won’t produce the result you are looking for.

Bad estimates reduce the productivity of builders too, since it can cause the project team to become angry and frustrated. People don’t work very effectively when they feel like they are in a no-win situation. In fact, estimating the work at all tends to reduce productivity.

Source: Peopleware: Productive Projects and Teams, 2nd Edition, Chapter 5