Hard vs soft constraints

[Fred45]

I have heard that you shouldn’t use constraints such as Must Start On or Must Finish On. My project has many of these and I would prefer not to remove them

[Intaver Support]

As a general rule, you should avoid using hard constraints unless for very specific reasons as they do not allow the project’s activities to update properly when changes are made to the schedule. This is especially important in Monte Carlo simulations because that is exactly what we are trying to measure, what will happen if some activities are delayed , take longer than planned, or alternatively start early or take less time. If you use hard constraints, you may end up with an artificially more optimistic result than you would have otherwise.

In the example below, even though both activities have the exact same estimates, because of the hard constraint, the first task appears to have less variance or risk which may not reflect reality.



There are cases in which hard constraints are justified. The case may be that a hard deadline exists for access to a testing facility or a launch window. These are “real world” constraints and sometimes and can be used if your team believes it is useful, though there are other methods, such as using deadlines with the Success Rate view that provide the same ability to measure the probability of meeting a hard deadline, without the use of hard constraints. In the example below, the Success Rate view shows that the activity has only an 18% chance of finishing before a set deadline.

[Intaver Support]

When you import schedule from Microsoft Project, you can relax some constrains. To do it click on File -> Import -> Map Microsoft Project Fields -> Advanced Mapping -> Change Constrains during import.

[Intaver Support]

Please be very careful with relaxing some constraints during import files from other scheduling software because it may cause incompatibility between schedules in RiskyProject and other scheduling software.