There are two great dangers in the Soul of Iron challenge: murlocs; and other players.
Soul of Iron is the "hardcore" challenge in WoW Classic Season of Mastery. You can talk to an NPC in Ironforge to get a Soul of Iron buff. The buff doesn't actually do anything, it's mostly for display purposes. If you ever die, you get a debuff that says what level you died at.
My priest, Vespertine, fell in Uldaman at level 42.
I was healing, but we accidentally pulled the entire room with the Steward Keeper boss. The one with the whirlwinds that slow you down. Between the boss, two extra golems, and five or six Earthen, we quickly wiped.
In hindsight, the fact that the tank was in the guild <UWU> was probably a warning sign.
(That's probably a little unfair, the tank was generally good, just cut a few too many corners.)
I was even in a Soul of Iron guild--unimaginatively called <Souls of Iron>--and sadly had to leave it. Even worse, another guildie was in that run, so he lost SoI as well. Ah well, those were the rules, and guild chat was full of "F" to salute the fallen, as per the tradition.
I'm not really sure what to do now. I could keep going with this character, playing normally. But I'm not very interested in endgame in Season of Mastery. I could delete the priest and reuse the name to make a new character, probably with a different class, and rejoin the guild and try again. I suppose I could just make a second character and put off the decision.
I did enjoy the Soul of Iron experience, especially being in a guild of people all trying the same challenge. If you want to try Soul of Iron, I recommend <Souls of Iron> of Shadowstrike.