I have come to the realization that the number three (3) is very significant to Elder Scrolls, both in and out of universe. Here are just some of the examples I kept coming up with while lost in thought unable to sleep last night. I am sure you guys who know more about the lore of the world and history of the games can probably think of a lot more. Some of these may be slightly inaccurate since I do not have a complete understanding of all the lore.

There are three Imperial dynasties in Tamrielic history leading up to the main game series: Alessian, Reman, and Septim.

There are three Tribunal god-kings of Morrowind: Vivec, Almalexia, and Sotha Sil.

There are three Great Houses featured in vanilla Morrowind: Redoran, Hlaalu, and Telvanni. This one is arguable because there are two other Great Houses of Morrowind, Indoril and Dres, which do exist in the world at the time of the game but have no territory or presence in Vvardenfell. If you consider that historically, there is a sixth significant Great House, Dagoth, this makes for two sets of three if you count them. They did after all exist as a proper Great House before they were eradicated after Vorryn Dagoth's betrayal of the other Houses. But in game, there are only the three.

There are three Imperial "Moth" forts in Bethesda-made Morrowind: Buckmoth, Moonmoth, and Frostmoth from Bloodmoon. This is arguable as some people count Firemoth being a former Imperial ruin and Bethesda-made even though it's just DLC and not a full expansion, but since it is a ruin the Imperials no longer control it so I really don't count it anyway, leaving us with three.

The third numbered game in the series, Morrowind, was the first to be developed with a hand-made world rather than procedurally, and also the first game in the series to enjoy mainstream success. Arena and Daggerfall had their fans but Morrowind is when the series really started to become popular. Additionally, Morrowind was the first of three numbered Elder Scrolls games, also including Oblivion and Skyrim, to gain mainstream popularity.

Morrowind and Oblivion each have two expansions, so each game has three major questlines. Skyrim breaks the pattern with three expansions, but that is still an instance of three of something.

There are three major Imperial career guilds: Fighters, Mages, and Thieves.

There are three assassin guilds featured in Morrowind and its expansions, even though only one is playable: Morag Tong, Camonna Tong, and Dark Brotherhood.

There are nine provinces of Tamriel. This does not technically break the pattern of threes as nine is three times three. Likewise, the Imperial religion is based around The Nine Divines.

There are three different Daedric helmets available in unmodded Morrowind.

Tamriel Rebuilt features three major Imperial cities currently in release areas: Firewatch, Helnim, and Old Ebonheart. I am aware of Cormar and explored it a bit during a recent flyover but do not currently count it because it is one of the "ghost towns" in Preview, quite unfinished, and seems to be a lot smaller than the three other cities I mentioned. Still pretty though.

Also considering Tamriel Rebuilt preview areas, there seem to be three little Nord villages between Baan Malur and Solstheim.

There are three special tools required to interact with the Heart of Lorkhan: Keening, Sunder, and Wraithguard.

There are three playable elf races: Altmer, Bosmer, and Dunmer. This one can be contested because the Orcs (Orsimer) are technically Mer as well but many players don't consider them like elves. These are also the only three elf-mer races still culturally significant in-game at the time of the main series, even though historically there have been many more mer-races that have disappeared from the world or are no longer significant.

There are three cities with booksellers in vanilla Morrowind: Ald-Ruhn, Balmora, and Vivec (technically two merchants there.)

There are 36 Lessons of Vivec (three times the number of months in the year.)

There are three named characters the player interacts with during character creation in Morrowind: Jiub, Socucius Ergalla, and Sellus Gravius. There is also a guard who talks to you directly but he just has the generic "Imperial Guard" name so doesn't count as a named character.

Vanilla Morrowind also features three types of Atronach monsters and thee types of Dwemer clockwork automotons.

Incidentally, three is the number of mod projects I am working on that are based on Tamriel Rebuilt. This does not actually count because it's multiple degrees of unofficial, just an interesting observation I had while thinking about this.

This is what I personally came up with, not an insignificant list at all, but as you can see the number three is very significant and keeps repeating itself throughout Morrowind and Elder Scrolls. Perhaps some of you know of other examples, feel free to share them if you want.