In the 16th and 17th centuries, before commercial fertilizer was invented, large shipments of manure were transported by ship. It was shipped in dry bundles because in dry form it weighed a lot less than when wet. But once water hit it at sea, it not only became heavier, but the process of fermentation began, a by-product of which is methane gas. It didn't take long for methane 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 somebody figured out what was happening. Once they determined the role that manure played in the explosions, everybody began stamping the bundles with the term "Ship High In Transit," so that the sailors would know 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 golf term.