One day I'll get all the project managers I can find in a room and give them a GCSE maths paper to complete. Every five minutes I'll tap them on the shoulder and say "Can you stop what you're doing and move onto question 10?" and "How is your progress going on question 5?".
Once every twenty minutes I'll make them sit in a small room and talk on a conference call where someone is screen-sharing a Jira instance with all the questions marked as Jira tickets and I'll ask them to t-shirt size each one.
Then, at the end of the three hours allocated for the paper I'll ask them to stop and explain why, when the estimated time for the paper was three hours, they haven't completed it.