Bob Lieberman's Blog


Things Take Longer Than You Think

If a chicken and a half can lay an egg and a half in a day and a half, how many eggs can a chicken lay in a day? Heard that one before? Hint: the correct answer is not 2/3.

As any farmer will tell you, only live (whole) chickens lay eggs, and no chicken can lay half an egg. So the premise is impossible – in the real world, arithmetic gives way to common sense. 

Now try this one: If a bank customer arrives on average every five minutes, and on average requires five minutes of a teller’s time, then how many bank customers can a teller serve in an eight-hour day, on average? Hint: the correct answer is not 96.

As any branch manager will tell you, the customer arrival rate fluctuates throughout the day. When there’s a spurt, tellers fall behind. When there’s a lull, if customers are waiting tellers can catch up. But when there’s a lull and no customers are waiting, tellers are left idle – and that idle capacity can’t be recovered. Again, arithmetic gives way to common sense in the real world.

The rule is this, from the mathematical discipline of queuing theory:
In any system where requests arrive and are processed, processors fall behind if average service capacity is equal only to average demand.
Your company, your project, your inbox, your todo list, and the highway you commute on – these are all systems. So whether you’re a project manager, clerk, house painter, traffic planner, or technical writer, you have to provide excess capacity if you hope to avoid falling further and further behind.

The good news is that the excess capacity not only permits you to meet commitments, it accepts the inevitabilily of idle time – so you can use it instead of fighting it. Idle time is useful for administrative tasks or just plain resting, but also for creative experimentation, relationship-building, and channeling frustration into productive strategy.

If you estimate 120 hours of work on that new marketing brochure, at 40 hours a week it will take you longer than 3 weeks. But you may get some great ideas while waiting for reviewers to read your first draft.
If you'll be driving 90 miles to a client at 60 mph, it will take you longer than an hour and a half. But you can listen to an audiobook or think up ways to have the next meeting on the phone.
The pattern can be summarized using just two words: “longer than”. Things always take longer than you think, because time lost can’t be recovered.

So if you want your company, your work, your hobby or your life to be more predictable in its consumption of your precious time, estimate more conservatively.

If you have executive responsibilities, the same advice holds true with those. Your company will only get ahead of its (huge?) backlog of projects if you give it more resources than you think it needs.

It does need them, and it's probably been taking them all along, anyway. Now you know why.