There are a few of us kicking around the forums and I'm kind of wondering what made you look at the class and go "yeah, I want to tank with that". This thread isn't to talk about viability of NB tanking in endgame/PVP/whatever, just a trip to the department of backstory. I don't care if you tank in PVP, vet trials, normal dungeons, spend all your time in zone casting Sap Essence on mudcrabs or if your NB tank just runs around picking NPC pockets these days, I'm just curious about what got you to try tanking on a NB, and why did you stick with it (if you did).
I've played RPGs of various stripes since the mid-90s but ESO was my first MMO (not counting
Kingdom of Loathing for obvious reasons) so I didn't know much about tanks, healers, or DPS, other than what I kind of gathered from hanging out with other gamers, many of whom did play MMOs. My first clear of Aetherian Archive (then v12 or v14 or whatever it was) as a stamblade involved Wrecking Blow spam.

I was actually going to roll a DK when I first got the game, because dragons are cool, but then I remembered how much fun I had playing Nightblades in Daggerfall and Oblivion, and NB was the closest to the "sneaky archer" archetype that I usually enjoy, so I decided to go with that. I leveled as a stamblade, but I kind of wasn't enjoying it. In older TES lore, NBs were swift, and agile, and good at magic, but archers in ESO are really not suited for magicka playstyles, unless you count the spectral bow NBs get from Focus. Magicka nightblade seemed like a strange idea at the time since my character is a Bosmer, who aren't really good at magicka type stuff (Jagar Tharn doesn't count).
As I was levelling, the bane of my existence was that Undaunted quest for Banished Cells (i am a completionist and I really don't like having quests sitting in my log unresolved, and I hate abandoning quests even more). I thought that it required me to clear the whole dungeon (I have yet to l2read quest descriptions, it's a lifestyle, don't judge), not just enter it and return to Turuk with the good news, so I spent hours hanging out outside the entrance to BC hoping someone would take me with them. This was long before Group Finder and I didn't know anybody in the game. Then I tried going in there on my own (wearing dropped green/blue gear, no sets). I died to the first trashpack, but hey, my quest had advanced. One thing I noticed during the waiting for BC was a lot of people looking for a tank.
I wasn't really used to the whole MMO community thing and I've always tried to figure things out on my own rather than look up guides, so the learning process for me was very slow. After I discovered sets and started training my character in crafting, I realised that i would be able to maybe use a set to make my character do what I wanted. I started looking at the skills and morphs and passives to see what I could do, and I saw that ESO nightblades had passives that got buffed by heavy armour use, so I thought, what about a tank? It went so counter existing TES lore, but I looked at the in-game description for the class:
Nightblades are adventurers and opportunists with a gift for getting in and out of trouble. Relying variously on stealth, blades, and speed, Nightblades thrive on conflict and misfortune, trusting to their luck and cunning to survive.
...and I kind of zeroed in on "trusting to their luck and cunning to survive" and thought, well, why not try and survive the biggest hits in each encounter? I could do that if I made a tank. Besides, judging from the never-ending stream of "lf tank for XYZ" in zone chats everywhere I went, there was plenty of opportunity in tanking.
By this time I was a lot more aware of just how complex an MMO is compared to a single-player game, so I was much less shy about googling stuff, so of course I googled Nightblade Tank and instantly found the sap tank, which was quite strong at the time. Joined some guilds, made some friends, chose some gear sets, started running group content. Never looked back, tbh, even though the sap tank is only a misty watercolour memory nowadays, and the NB tank identity is being stripped away little by little with every update. I learned to tank on a NB, started out strugglebusing for hours on Grothdarr, and at this point I've cleared nearly all vet content, including many HM trials, on my NB. Due to lack of time IRL I can't quite drum up the interest to tank on anything else. I moonlight as PVP and PVE heals and fair-to-middling mag DPS on the same character via gear and CP swaps, so I'm really kind of a Swiss Army Nightblade, but I don't love anything in ESO as much as I love tanking on my NB.
Okay, maybe fishing. I really love fishing.