In the 16th and 17th centuries, most things had to be transported by ship. At that time commercial fertilizers were yet to be developed, so large shipments of manure were common.
Manure was shipped dry, because in dry form it weighed a lot less than when wet. However, if water hit it, it not only became heavier but the process of fermentation began again, of which a by-product is methane gas. As the manure was stored below decks in bundles, methane would build up below decks. The first time someone came below with a lantern, BOOOM !!!
Several ships were destroyed in this manner before they worked out what was happening.
After that, the bundles of manure were always stowed high enough off the lower decks so that any water that came into the hold would not touch this potentially volatile cargo and start the production of methane. The instruction “SHIP HIGH IN TRANSIT” was stamped on the bundles to remind the sailors to stow it high and keep it from getting wet.
Thus evolved the term “S H I T” (Ship High In Transit) 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.