In the 16th and 17th centuries, everything had to be transported by ship. It
was also before commercial fertilizer's invention, so large shipments of
manure were common. It was shipped dry, because in dry form it weighed a lot
less than when wet, but once water (at sea) hit it, it not only became
heavier, but the process of fermentation began again, of which a by-product
is methane gas. As the stuff was stored below decks in bundles you can see
what could and did happen. Methane began to build up below decks, and the
first time someone came below at night, with a lantern, BOOOOM!!!

Several ships were destroyed in this manner before the cause was determined.
After that, the bundles of manure were always stamped with the term," Ship
High In Transit" which meant for the sailors to stow it high enough off the
lower decks so that any water that came into the hold would not touch this
volatile cargo and start the production of methane. Thus evolved the term
"S.H.I.T," which has come down through the centuries and is in use to this
very day.

You probably did not know the true history of this word. Neither did I. I
always thought it was a fishing term

Now You Know! Joe McIntosh