Murphy's Law was first cast by Joe Chase, Editor of the Flight Safety
Foundation's mechanics Bulletin in early 1955. It grew out of the precept
developed and published by the foundation in its design notes
that "Procedures for adequate maintenance and operation practices
established by designers should be consistent with average human effort,
ability and attitude". The law coined reads: "If an aircraft part can
be installed incorrectly, someone will install it that way."
Corollaries to Murphy's Law have sprung from all over the industry.
Here we present some examples:
- If anything can go wrong, it will.
- It is impossible to make anything foolproof because fools are so
- An experiment may be considered succesful if no more than 50 % of
the data obtained must be discarded to get a result which satisfies
the theory to be proved.
- No experiment is a complete failure. It can always serve as a bad
- When all else fails, read the directions.
- Specified environmental conditions will always be exceeded.
- Any error that can creep in, will. It will be in the direction that
will do the most damage.
- All constants are variable.
- In a complex calculation, one factor from the numerator will always
move into the denominator.
- In any given computation, the figure that is most obviously correct
will be the source of error.
- In any given miscalculation, the fault will never be placed if more
than one person is involved.
- Dimensions will always be expressed in the least usable terms.
- Interchangeable parts won't be.
- Any wire or tube cut to length will be too short.
- Identical units tested under identical conditions will not be identical
in the field.
- Availability of a part is inversely proportional to the need for the
- The easiest way to find something you lost is to buy a replacement.
- Don't force it. Get a bigger hammer.
- If you don't understand a particular word in a technical article,
ignore it. The text usually makes perfect sence without it. (With
the exception of Maskinelement books, of course.)
- Make three consecutive correct guesses and you will establish
yourself as an expert.
- A man who can smile when things go wrong has thought of someone he
can blame it on.
- A dropped tool will land where it can do the most damage. (Also
known as the law of selective gravitation.)
- The accessibility of a part which falls from the workbench varies
directly with the size of the part and inversely with the importance
of the part in completing the job.
- Tolerance will accumulate unidirectionally toward maximum difficulty
- Hermetic seals will leak.
- After an instrument has been fully assembled, extra components will
be found on the bench.
- After the last 16 mounting screws are removed from an access plate,
it will be discovered that the wrong access plate has been removed.
- Any safety factor set as a result of practical experience will
always be exceeded.
- Components that must not and cannot be assembled improperly will be.
- The probability of a dimension being omitted from a drawing is
directly proportional to its importance.
- The most logical way to assemble components will be the wrong way.
- The more innocuous a design change appears, the further its influence
- The necessity for making a major design change increases as the job
- A part will be made exactly as specified in a drawing only when the
drawing has an error.
- After all, there is a Murphy in every crowd.
- No job is so simple that it can't get screwed up.