A checklist that's too long overwhelms users. A checklist that's too short misses critical checks.
A good rule of thumb suggests that 5-9 items work well for most routine tasks. For complex procedures, aim for 15-20 items maximum.
Beyond 20 items, people can start to rush through checks or skip items entirely. The checklist loses its protective power.
If your process requires more checks, break it into multiple focused checklists. Each checklist should cover one phase or aspect of the task.
Remember: the goal isn't to document every possible action. The goal is to catch the critical items that are easy to miss or forget.
Focus on the vital few, not the trivial many.