Discuss what you once believed or assumed, but later discovered to be wrong about lore and/or game mechanics. Or what you once ignored and didn’t find out until (much) later.
Me first: I once mistook Mrs Plenty for a Master. Before I saw her name, I had already found that most human characters are not referred to with their names, and that Masters are certainly non-human and have names like “Mr (a common noun)”. So “Mrs (a common adjective)” seemed quite likely to be another Master… 
I ignored opportunity cards completely until I was mid to late POSI. Like all of them. I had to do some much lower level stories once I acknowldeged the issue and raising connections was quite the bother since I was doing it at a point when I was “supposed” to be somewhat further along.
Back in the days when I started playing, I was thinking that FL is a multiplayer game. Because almost every browser game is. Why build it in on a single common server otherwise.
Is Fallen London an MMORPG?
Well yes, but actually no (no?)
I took the existence of Hell entirely literally and avoided devils like the plague. Sometime around ‘Cricket anyone’ (so lik 4 years into playing) my brain suddenly clicked and went ‘Ohhh they’re bees!’
I mean, they’re bees who want to trade for your soul so the infernal explanation wasn’t totally unfounded 
You know the Soft-Hearted Widow? The one who gives you a home at the very beginning of the game? Well, I had her confused with the Gracious Widow, the criminal mastermind. Now, that would be easily correctable and not mean much, but when I was asked to give a toast for that one shadowy alignment quality, I chose the gracious widow, thinking that such a nice woman deserved a toast. So imagine my surprise when the guy you are talking to pales and shrinks away from you in fear and my Heartless increased. Also you can never change who you toast too, unlike the other alignment qualities.
I reached the exact same wrong conclusion for the exact same wrong reason re: Mr Inch.
Took me quite a while to realize the Gracious Widow is not the Duchess.
At least, that is what I am thinking now.
Apparently there’s a starter boat that’s relatively easier to get once PoSI is reached and I didn’t have to grind for difficult items for the better part of a month? I’m only going by what I’ve read on the forum and Tumblr and whatnot, I don’t even remember seeing the option. I don’t regret making my first boat the Swift Zee Clipper though (although now I’m the proud owner of a Nyx-class zub)
Yeah. Wow. I completely missed this.
I thought that for example, the Dirigible icon was a snake with a hat, the honey picture was in a cone thing, there might have been more. Also I didn’t read most of the text, that was a VERY BIG mistake
To ignore opportunity cards is quite common on mobile phone… especially when players unlock some new content like crowds of spite or laboratory. Besides, during this year’s Fruits of the Zee Festival, some people spent quite some time to discover the Pentamerous Bride, because she was not on any card but a storylet.
I somewhat mistook the Extravagantly Titled Tigress’ tiara as a maid headdress, and several friends were surprised to learn that it is not.
I came across the mobile app (before it was retired) before I found the browser version of the game and thought the app was the only version of the game – and was very, very sad that it wouldn’t install on my very old and creaky phone I had at the time. It was weeks before I found out that not only was the app not the only version of the game, it wasn’t even the primary version.
When I saw the Decemberist’s Pocketwatch on the wiki, I knew nothing about Calendar Council, and therefore thought of Russian history and Pushkin… But this Decemberist is not that Decemberist.
When I first dived into the Waswood, the event was Virginia at the Fruits of the Zee. My, I mistook that orphanage for THE Orphanage in Light Fingers (you know, the mask, the sound of it and all that), and it frightened the hell out of me.
Well, it is, actually. I don’t know of any conventional orphanages where workers wear creepy white masks.
Oh jeez the nightmare continues…
Now I’m thinking whether it’s an actual misconception…