What is the safest way to fix a broken demo?  Hide all bugs
with local patches, as workarounds to special cases.

Handle only the specific circumstances seen by the demo; ignore
other implications.  Add special branches to the logic.  Hide
exceptions and errors that might reveal deeper problems.  As
long as side-effects are not visible in the demo, you will be
congratulated.

If you try to clean up defective logic at the source of the
bug, you might expose bad assumptions elsewhere.  You do not
want to spoil the next presentation, do you?

A demo follows a carefully planned "happy-path" "thin-thread"
workflow through an application, with the same order, data, and
options each time.  You know where the demo will encounter the
bug each time.  Apply a bandage to the exact spot.

You can even pretend you are being Agile, because you are
solving one problem at a time for a user.  You have only one
user who matters -- the one who gives the demo.

Unfortunately, real users can exercise the full application and
try options in different combinations.  A customer will
rediscover any faulty logic.

When you ship, plan on a limited rollout to receptive
"early-adopters" in a controlled environment.  Think of it as a
hands-on guided demo.

Bill Harlan, August 2009