It would be fantastic if we knew the future. With that knowledge we could plan with the utmost precision. But we are not clairvoyant. We actively exercise a process of guesses we dress up in the fancier name of "estimates". Enrico Fermi would feel these guesses are fine so long as you are within an order of magnitude. This form of educated guess is also known as a "back of the envelope" calculation and most random guesses are not doing anything near this level of rigor. Back of the envelope calculations take rough approximations, simplified assumptions, and various tidbits of top-of-the-mind knowledge to calculate a ballpark figure.

Put yourself in the shoes of a manager of a team and imagine asking each person
in this team "how long do you think this task will take to finish?" This could
well be *any* type of task. Estimations may sometimes vary wildly and sometimes
group around a certain value. Any kind of grouping is a coincidence. Asking the
same person about an estimate even the next day may yield different results. How
could you help improve the accuracy of these estimations with such fluctuating
results?

One option is to decide on all the work you expect upfront. If you know how work
is subdivided *exactly* you'll know, transitively, how long the total task will
take, right? Wrong.

Instead you'll starve people of autonomy around how they can tackle a goal. Starving autonomy means people stop thinking and now you'll have to work even harder to keep everyone productive. It also makes people unhappy, whether they realize it or not, and you'll probably wind up with a great deal of turnover because of it.

What about using time taken from similarly sized tasks? If it took someone a certain number of time to complete a task with a rough "t-shirt size" then it ought to take another, or the same, person roughly the same, right? Wrong.

Even if you had the same person doing the same task there is the possibility that some spontaneous act can change timings drastically. People get sick. Their dependents and partners get sick. Trains get delayed and vehicles break down. The human brain decides to watch a video for an hour instead of fifteen minutes. A meeting that was scheduled for an two hours only takes one.

We tend to attach degrees of confidence to our guesses but never seem to discuss
those confidence levels openly. We also tend to wrongly consider tapered
ranges as
the more accurate guess. We feel pressured to pick the most likely range and
make it a promise. **Resist this temptation and try making this range of
possibilities explicit.**

Many people focus on what kind of confidence they back on a single range, but
our confidence may differ between slices of respective intervals of time. **Try
to consider that your confidence in your guesses is not a normal distribution
centered around a single range; Confidence may be distributed in any number of
ways.** There may be a high probability that the job gets finished if we focus
on it at the beginning and the end of the year, but a low probability otherwise.
If we have the time to work on this task on the fortnight's the probability goes
up, but the likelihood of completion dips on the weeks in-between.

Does a low probability mean impossibility? No. Nor does a high probability imply absolute certainty. A range of probabilities discusses the full spectrum of what might be feasible. It is better to know you think a project might take only a months work of time all the way up to six months than it is to merely work under the assumption that the single month would do.

**Make back of the envelope calculations by decomposing problems into
constituent parts.**. The refinement of the accuracy of these parts refines the
overall estimation. This isn't to say breaking down a random guess into several
random guesses will improve accuracy. In fact, with the random-guessing approach
you will probably be reluctant to go below a certain lower-bound, which means
that a decomposed guess might far exceed the original guess. Back of the
envelope calculations try to tie you to real facts, although possibly
simplified, without believing the hype that you can estimate down to the minute
based on prior similar scenarios (see above). Machine learning won't save you.
The great thing about back of the envelope calculations is that they work
equally well for both high- and
low-level
concerns.

**Pretending estimates given on work are guarantees is fool's gold.** Push back
on demands for promises when you know you are only making a guess. We might get
better at making guesses with time by practice and research but a guess is still
a guess, educated or not.