I fancied myself a rationalist. As a philosophy major I learned to prize reason over emotion, knowledge over belief. It was my opinion that the law ought to extract as much emotion as possible out of the trial process because emotions led to things like prejudice and misplaced sympathy, and generally allowed lawyers to manipulate the system to get what's best for their client, regardless of what's best for society. Your first lesson was that law, and especially trial practice, is about more than just the facts.
Facts are often indeterminate.
As the Necker Cube illustrates, reality can appear very different depending on how you look at it. Juries can't simply enter the facts into a computer and spit out the right decision, they must make tough decisions, sometimes life and death decisions. A trial is a process for making those tough decisions while giving the appearance of justice. It is a rhetorical framework to convince the people of the rightness of the outcome, even though the truth, the factual truth, is unknowable. The rules of evidence are designed to protect the credibility of the process.