If anything can go wrong, it will.
Nothing is as easy as it looks.
Everything takes longer than you think.
If you perceive that there are four possible ways in which a
procedure can go wrong, and circumvent these, then a fifth way
will promptly develop.
Whenever you set out to do something, something else must be
solution breeds new problems.
Nature always sides with the hidden flaw.
Firmness of delivery dates is
inversely proportional to the tightness of the schedule.
a project requires 'n' components, there will be "n-1" units
A failure will not appear till a unit has passed final
A purchased component or instrument will meet its specs long
enough, and only long enough, to pass incoming inspection.
Wethern's Law of Suspended Judgment
Assumption is the mother of all screw-ups.
Laws of Revision
Information necessitating a change of design will be conveyed to
the designer after
– and only after the plans are complete.
The more innocuous the modification appears to be, the further
its influence will extend and the more plans will have to be
If, when completion of a design is imminent, field dimensions
are finally supplied as they actually are
– instead of as they were meant to be
– it is always simpler to start all over.
There is always an
easier way to do it.
When looking directly at the easier way, especially for long
periods, you will not see it.
No matter what goes wrong, it will probably look right.
When an error has been detected and corrected, it will be found
to have been correct in the first place.
experiment works, something has gone wrong.
In any collection of data, the figure most obviously correct,
beyond all needs of checking, is the mistake.
No one whom you ask for help will see it.
Everyone who stops by with unsought advice will see it
Stewart's Law of Retroaction
It is easier to get forgiveness than permission.
Gilb's Third Law of Reliability
Investments in reliability will increase until it exceeds the
probable cost of errors, or until someone insists on getting
some useful work done.
90% Rule of Project Schedules
The first 90% of the project takes 10%t of the time, and the
last 10% takes the other 90%.