Certainty? In this world, nothing is certain but death and taxes.
In the modern mystery, death is usually a critical element, a certainty. If there isn't a body somewhere pretty early on in the story, most mystery readers get a little itchy and twitchy and wonder what's up. And, truthfully, I love exploring death (fictionally speaking). I can spend endless hours researching sneaky ways to kill people circa 1880 and thereabouts, and I love setting up and (ahem) executing the murder scene(s) in my books.
However, regarding the second half of Benjamin Franklin's observation, all I have to say is Bah!
I have a technical/scientific background, so you'd think that taxes would be a snap, right? It's only numbers. It's math. It's logic. For heaven's sake, we're talking basic arithmetic here—add, subtract, multiply, divide—not calculus or complex number theory. The financials of my writing/editing consultancy business (which includes my fiction efforts) should theoretically be neatly bound, gagged, and overdosed with Quicken and Excel. All those little numbers showing profit and loss, income and expenses, should be subdued and ready for delivery well before mid-April.
Unfortunately, my financial process is akin to my process for researching methods of death and destruction. Usually, when researching for fiction, I'm bouncing from book to book, website to website, landing on random facts, thinking "hmmm, that's interesting, and perhaps useful," stashing it away mentally (or on a random sticky note) before zipping off in another, tangential direction. In the financial realm, my approach is similarly random. Receipts are crammed willy-nilly into my wallet until the wallet is too full to close, whereupon the crumpled bits of paper are regurgitated into a paper bag (yes, that's what I said, a paper bag). Now, the wallet is free to feed again, and the process repeats. As for statements, consulting contracts, and so on, they alight on whatever surface is at hand upon my entering the house. There they linger, to become buried beneath equally important papers, until I can corral them into the all-consuming paper bag.
When the time comes to "deal with it," the paper bag is emptied onto the dining table, which cannot be used for dining until taxes are done.
In fiction writing, it's fun to toss motives, method, characters, location and era all into a big jumble, shake 'em up, and see what comes of it.
Unfortunately, the same process when applied to taxes does not yield a very satisfying result.
And that, dear Benjamin, is a certainty.