In the final days of sail powered commercial shipping, 25 out of every 100
ships sank at sea -- usually from hitting rocks in limited visibility
conditions -- before being taken out of service due to age, about 20 years.
one in four ships sank before retiring (according to Royce).

In fact, recreational sailboats (and powerboats) often hit the rocks in fog or
rain, thinking they were somewhere else on the water, until the advent of Loran
and later GPS (becoming more common on boats starting about 25 years ago).

Wandering around in a fog or driving rain is stupid and irrational, so sailors
just convinced themselves that they personally were smarter than the gods and
the laws of physics both.

DR is, in fact, "navigating" by pointing yourself in some direction, then
moving what you think is in the direction at some speed relative to the air and
water around you for some period of time, and then convincing yourself that you
ended up exactly that far in that direction, less some fudge factor based upon
a guess as to water and wind movements. (think of walking in a large field, a
helmut over your head that shows you only what direction you are pointed, a
clock and a counter for the number of steps you take).

Obviously, that is a truly dangerous thing to do with rocks in the water, and
prudent mariners of the day stood offshore until the weather improved. stew
ped marines, on the other hand, hit the rocks and sank, or *if* they got very
lucky indeed and missed the rocks convinced themselves the gods and laws of
physics don't apply to them.

Now, because DR in and among rocks is so stew ped, armchair sailors and those
who only occasionally get out on the water and those who have been lucky -- so
far -- decided to "expand" the definition enough to make it look as if they
really, really, really weren't stew ped for wandering around in a fog. They
changed the definition to included landmarks, and still call this "deduced"
navigation (* see below). these rather indiotic, buy non-sailing, sailors
called DR something like this. You stand on the corner of 1st and Elm, walk to
5th and Elm, turn left and walk past Maple to Oak, turn right and walk to 7th,
turn right to Maple and you are there. Nevermind that they deduced not a thing
at all, they had a known (and knowable) position every step of the way. Now,
they feel safe when they are out in a fog or driving rain, for no rocks can
search them out to sink them.

* some armchair and/or limited experience sailors changed the definition of DR
from Deduced Reckoning to Dead Reckoning (the word dead as in dead even, or
dead on center or dead (as in flush) as a doornail) than thus instantly --
though obviously completely erroneously -- make their position on the water in
a fog or driving rain to be nowhere near any rocks.

Now, because armchair and/or limited experience and/or very lucky sailors
intuitively KNOW that wondering around in the fog or driving rain is stew ped,
they feel oh so much more comforted when they lie to themselves and tell
themselves that the gods and a laws of physics don't apply to them.

But remember, in the final days of commercial sailing vessels (manned by highly
experienced, professional mariners) one ship in four sank before being taken
out of service due to old age (about 20 years).