"I don't have a pot of gold, I'm an accountant. Please stop poking me."
Back in the late 1800s, a Scottish fellow named David MacRitchie hatched the theory that the fairies in British folklore probably traced their roots back to a race of people who lived alongside early Brits -- a pre-Celtic race of tiny people. Willow and his village, if you will. But you won't, because that's silly.
MacRitchie believed that a race of pygmies lived in the U.K. way back when, and there was a "folk memory" of their existence passed down and changed through stories over the generations that made them into the fairies they became. This entire theory hinges on the idea that you can have a race of midgets just living in your country and wipe them out completely without any evidence that they ever existed, anthropological, archaeological, or otherwise, beyond stories of tiny men cobbling your shoes at night and the script for the movie Legend.
MacRitchie tried really hard to make this theory work, going so far as to find support for an argument that any reference to giants in folklore was metaphorical and just meant giant in their tiny awfulness. Unfortunately, our knowledge that people who existed before us tended to always be people as far as archaeological evidence goes does poke some holes in the idea, along with the lack of any tiny man fossils that might suggest an entire tiny race ever existed there. But hey, just because you can't prove something ever existed doesn't mean it never existed, it just means you should maybe question why you think it existed based on a total lack of evidence beyond assorted fantastical stories that were not geographically limited to your corner of the world in any way whatsoever.
The Loch Ness Monster Is a Plesiosaur
Likely everyone who has heard of the Loch Ness Monster has also heard the most popular theory about what it could be among those who think it's a real thing -- a plesiosaur. What's a plesiosaur? It's like a dinosaur from the Jurassic period, meaning it would have died out over 65 million years ago, more or less, along with the rest of the beasts that existed at that time. Except for that one in Scotland.
Every picture and sighting of the Loch Ness Monster describes this big, long-necked, massive-bodied plesiosaur-like beast, so why not simply assume it's one of those things? Maybe in the depths of the loch a family of them somehow survived and thrived and avoided death and destruction for millions of years. And then it also forgot that fossil records show that plesiosaurs did not have flexible necks but rather really tightly connected neck vertebrae, so all those sightings of a long, curved neck like a snake or a swan were just tricks of the light or caused by Nessie after suffering severe whiplash. And films that show the beast paddling along just indicate that it also forgot about how a plesiosaur didn't swim with a paddling motion at all because its bones aren't connected that way and it would have been more like wings flapping. If you lived for 65 million years in a Scottish lake, maybe you'd forget how you were meant to swim, too. It's possible. And just because science at the time those images and films were made actually supported the curved, snake-like neck and paddling swimming motions and it wasn't until fossil reconstruction later on that it was proved that plesiosaurs didn't look or move like that doesn't necessarily indicate total, filthy fraud on the part of so-called witnesses at all. It just really suggests it.
It's not lying, it's just giving a hand job to the truth.
The biggest issue with Loch Ness, as opposed to other myths like fairies and werewolves, is that it's geographically constrained. Say you saw a werewolf in Romania and it's possible it ran away and now lives comfortably in the South of France. But a lake in Scotland is a lake in Scotland, and when you take a boat and do a complete sonar scan of the entire thing and find no giant, prehistoric beasts at all, it's not like you can just assume the monster packed its bags and headed to Vegas for a weekend. The stupid fish just doesn't exist. So even entertaining the idea that it was a plesiosaur isn't trying to use science to explain it anymore, it's following the trail of Reese's Pieces some bonehead with a camera and a model dinosaur left for you.
If there were dinosaurs in the lake, wouldn't you need a fairly decent breeding population for them to have lasted this long? Which is to say more than one? One dude can't hump himself for 65 million years. That's straight up crazy. Wouldn't dead ones wash up all the time? Wouldn't they have eaten the loch free of fish generations ago? Wouldn't this not fall apart under even the weakest of scrutiny?
To put it in very basic terms, there's no monster in the lake, there has just been a chain of liars. Not people making mistakes, not crazy people, just liars. Everyone who has ever claimed to see the Loch Ness Monster is a liar. So science doesn't even need to try to explain it with awkward stories of a kind of dinosaur that doesn't even fit the description once you actually know the science behind it. It's a lie.