When planning a project, we think about how long it will take to complete it. This is what we ask our team members: how long for you to code this module/wire this house/print these brochures?
We forget how hard it will be, how much effort we will have to put into the task to complete it.
- It may take 3 days for paint to dry, but there is not much effort involved in this.
- It may take 3 days to code a module, for a team of 3 developers who will have to rewrite part of the software core to make it work.
Same duration, different effort.
If something has a high level of difficulty and requires a lot of effort, the risk of delay is much greater, and you should plan for it in your schedule, that is, how long you allow for the task to be completed.