The Series 3 episode 'Gordon and the Famous visitor' reveals that Gordon believes that engines without domes are 'not respectable'. It's worth noting that Flying Scotsman (Who, in the books, was Gordon's brother) was exhibited at the 1924 Wembley exhibition alongside a much smaller express locomotive with no dome, and this loco was proven to be the more powerful of the two engines, so Gordon's dislike for domeless engines may just be an act of jealousy.
Fast forward to the Series 7 episode 'Gordon and Spencer', where Gordon begins to take a dislike to Spencer before even getting to know him. Spencer has no visible dome.
James is shown to be very proud of his red paint. While this is logic is lost in the show, in the original books when James was first introduced, all the current engines in the Fat Controller's railway were blue (Henry, who similarly was pompous about his green paint at first, asked to be painted blue as sign of humility, and asks for green when he becomes conceited again later on). This also explains why James is furious at the idea of being painted blue. His red paint makes him individual and unique in a band of similar engines.
Also in the original books, James was originally black, not unlike Donald and Douglas. It's a bit analogous to a teen having just left a school where uniforms are mandatory, transferring into one where they aren't, but a "non-compulsory" uniform exists. James is tired of being "just another" engine.
At first this troper wondered why Diesel 10 needed Paxton to help him steal the Christmas decorations in season "The Missing Christmas Decorations", despite being the only one able to do so thanks to his claw. But then, the one time Paxton refused to go along with him, Diesel 10 was caught in the act by Percy who happened to pass by. Diesel 10 needed Paxton to keep watch while he does the dirty work. Without him, the whole plan would've gone to pieces much quicker.
First and foremost—how in the world did the engines actually come alive?
Though the later seasons have slipped on this a bit (more and more after each), the engines really can't do anything without humans helping them. They need a driver and brakeman to move, the foundry crew to keep them in good repair. The possibility for blackmail is enormous.
Which leads to a disturbing afterthought, just who exactly would be steering the likes of Diesel, 'Arry and Bert as they menace the other engines?
On a similar note, take away the cutesy elements of the show, and it's really pretty apparent that the engines are in slavery. Even though they're fully sentient, none of the humans seem to carenote Though Sir Topham Hatt is generally fair and sympathetic, he is still, essentially, the 'master' He got very upset with Percy and some of the others in 'The Deputation,' for instance, when they tried to interfere with his decision-making process.. They've been bought and sold, banished for minor offenses, callously separated from 'family,' have no say whatsoever in where or how they work, they're automatically blamed when things go wrong, and don't appear to ever get any R&R.
Mentioning of the engines getting rest is mentioned every once in a while, even if it usually means another engine working twice as hard to compensate. Thomas and Toby have both been shown given whole days off, only to be guilt tripped by the other working engines into doing their jobs anyway. Granted it helps a lot that the engines actually seem to enjoy most of their work in moderation.
According to the Word of God, most of the characters are at least 20 years old, and some of the narrow-gauge engines are more than 100. They've been putting up with that crap for a long time.
Then there's the whole thing with scrapping. Edward and others occasionally work in the scrapyards and smelter's yards, where the engines are taken apart and melted down. The scrapyard tracks are lined with literally dismembered engines. Think, for a second, how badly most people would be messed up by seeing the human version on a battlefield or crime scene, and how many years of counseling they would need to attempt to get over that. The engines get no such sympathy.
A few of the diesels— Iron 'Ary and Bert—actually seem to enjoy working in this sort of "funeral home" so much that they tried to scrap Stepney, just for fun.
The real kicker? Word of God sets the show in the 1950s. Anyone not in the movie is likely in a scrapyard or worse. And most of the humans are gone too.
The Logging Locos from the special Misty Island Rescue were apparently sent away to the titular island because of their bad behavior. Judging by the abandoned state of the island's railway, the fuel shortages, and the dilapidated states of the three when Thomas discovers them, it quickly becomes apparent that they weren't sent there to do work, but to die.
There's an episode where Thomas's driver tells him that he's doing so well that soon he won't even need a driver anymore! Thomas takes this to heart and goes out on his own the next day... an adventure that is soon over when he crashes through the wall of a house. So basically, don't ever take responsibility for your actions or do things without an adult's help, even if they encouraged you to do it, because you'll cause destruction and possibly death.
The Flying Kipper is creepy enough, even without Fridge Horror, but there's a very dark Freeze-Frame Bonus if you're paying attention: There are three men in the brakevan that Henry smashes into, but only 2 of them are mentioned jumping clear of the wreck.
May be an oversight, since the original novel mentions all three shooting out when Henry crashes (the driver is left tending to both whining firemen in a comical fashion, implying all three came out fine).
Even worse: That story was based on a real life accident in which 14 people were killed.
In 'Ghost Train', Toby says "Percy's had an accident" as well as "It looked like Percy's ghost". Toby is basically implying that Percy died. This was just part of their trick but Thomas treats it as if it happened. His reaction is "Huh, who cares?" Thomas and Percy are meant to be best friends by the way.
This Troper is under the assumption that Toby was talking about a ghost Percy had been joking about earlier.
New train engineers are often told that at some point in their career their train will kill someone. These accidents are almost never the train crew's fault - people try to beat trains over crossings,play on the tracks, or just commit suicide. This is traumatic enough for someone sitting in a cab; many engineers suffer from PTSD, and a few have even taken their own lives. Now imagine being a sentient engine able to feel the metal crumple under your buffers. How many engines have been traumatized with the knowledge that they accidentally killed someone?
The station master's house that Thomas crashed into. You can only wonder why a house was placed that close to a train track meant to capture a runaway train.
Similar cases are shown throughout the series, such as a barber's house and a chocolate factory. Worth noting that none of them even have buffers, just a track leading straight towards the building. Tempting Fate enough?