Shit!

Shit is a vernacular word in Modern English denoting the feces,
the solid by-product of digestion. It is an old and native English word,
but following the Norman Conquest, Norman, Anglo-Norman, French,
and Latin terms for many common objects and bodily functions
began to be seen as more distinguished than native words.
And thereafter 'feces' became the accepted English noun,
'to defecate' became the accepted English verb,
and Shit was no longer used in polite company.

Bullshit, also bullcrap, bullplop, or horseshit,
is a common English expletive. It can also be shortened to just "Bull",
and in polite use, it is referred to by the euphemism BS.
Most commonly, it describes tautological, incorrect, misleading,
or false language and statements. Literally, it describes the feces of a bull.
As it contains the word "Shit" the term is usually considered foul language.
In British English, Bollocks is a comparable expletive.
The earliest attestation mentioned by the Concise Oxford Dictionary
is in fact T. S. Eliot, who between 1910 and 1916 wrote a poem
to which he gave the title The Triumph of Bullshit.
Written in the form of a ballade, the first stanza goes:

Ladies, on whom my attentions have waited
If you consider my merits are small
Etiolated, alembicated,
Orotund, tasteless, fantastical,
Monotonous, crotchety, constipated,
Impotent galamatias
Affected, possibly imitated,
For Christ's sake stick it up your ass.

The word Bullshit does not appear in the text of the poem.

"Shit happens" is a common slang phrase, used as
a simple existential observation that life is full of imperfections,
or "C'est la vie". It is an acknowledgment that bad things
can happen to people for no particular reason.
Shit!