I admit, I would be greatly confused by Julius Caesar quote as the term "trivial" has had different meanings throughout the centuries.

Today people associate the term "trivial" with minor details. For example SteemIt sees the votes of small accounts as trivial and blows the trivial votes off as dust.

Some would associate the trivial with trivia. Trivia are petty facts that fill our heads that only matter on Jeopardy and the Cash Cab.

With this definition, Caesar's sentence would be: The trivial stuff that doesn't matter in life matters in war.

In classical logic, trivial often meant related to The Trivium. The three legs of the trivium are grammar, logic and rhetoric.

NOTE: mathematics still uses the term trivial in the classic sense. A trivial proof is a proof that flows readily from the axioms of a mathematical system.

As Caesar would have received a classical education, I suspect that his definition of trivial would fall along classical definition. So the sentence might mean that the epistemological details presented in Trivium play a consequential role in war.

Yes, I would have been caught up on the term "trivial" as the different definitions have a non-trivial effect on the meaning of the sentence.