I think the universal rule is that when you kill a main character what you should be thinking is one of two things: “I really don’t want to kill this character but I have to for the story to work” or if it’s WH40k or A Song Of Ice And Fire “All humans die. Not all of them truly live.” And the later is because that’s what they’re thinking too.
“Men of Tanith! Do you want to live forever?” Is what Gaunt yells to inspire the Tanith First And Only. And then they cheer and they go over the top to rush the enemy trenchline because they do. Because, well, Saint Sabbat died gloriously and millennia later we’re seeing the Sabbat World Crusades and in its darkest hour Saint Sabbat comes by and she charges a Baneblade with a sword and a tube charge by herself and she wins because she’s Living Saint and as the one in Dawn Of War Soulstorm tells you when you click on her, “I died for the Emperor. And by his will rose again!”
Doubtless Sabbat could have had a nice and comfortable life and lived to 170 until she couldn’t afford another round of rejuv and died surrounded by grandchildren and everyone in her hometown would weep at her funeral. And that’s what many people would choose and they aren’t wrong to do so. Sabbat chose otherwise, and she died young and painfully and she lives forever. And so when a colonel in the Verunhive Primary sees one of Heritor Asphodel’s Woe Machines breaking through the gate to allow the teaming swarm of millions of maddened cultists to get in beneath the Void Shield protecting the primary hive spire, he grabs a ton of explosives and he yells his version of “Come on, men*! Do you want to live forever?” And he runs straight at the Woe Machine and he blows himself up and disables it to jam the gates. And he doesn’t get to be a Saint but he does get to have the Bell Of Lost Souls on Holy Terra toll in his honor.
So you can easily go through characters like a woodchipper and the readers will love you.
But if you are thinking “well I’ll kill this character because death makes readers cry” then probably you don’t really care about that character, and readers will see that and they’ll either not care either or they’ll drop the book right then and there and give you a one star review.
And it’s my opinion that while I know this because I love digging into literary theory, everyone in the thread knows it too, and that’s why while I’m going on for paragraphs, everyone else’s posts have generally agreed that you should kill characters sometimes but not always.
Also, I got in an argument on another forum with someone who made freemium games and I told him that I understood the economics but I only play Fate Grand Order and I won’t pick up another one, and he proceeded to explain the concept of using loot boxes to entice players, and because I’ve been out of sorts and rambly and I’ve been in several different simultaneous debates where people responded to me saying something by telling me something I already knew and this time I didn’t at least partially agree with their position I snapped
I told him I knew everything he told me already because I’m not an idiot and I’m not going to play another freemium game because their “welfare 4*” would not be Shiki Ryougi. Then I calmed down and explained that free players call them welfare 4s because every big event has a headlining random drop 5, but because the practices he described to fiddle with odds behind the scenes are illegal in Japan we just look at the mandatory odds tables and we see there’s a 1.00% chance a 5* will drop we don’t realistically expect to get it. So then I described the one from the first Christmas event, who is basically the cool badass evil version of the franchise poster girl Saber (who is on the poster decked out in full plate mail with her glowing sword in her hands so she is my mom’s email avatar now) and it’s a hogfather imitation. So the Welfare 4* is straight up her except she swaps her jet black platemail for a jet black santa outfit and she’s holding a santa sack over her shoulder and has her black and red sword in her hands so, you know, she’s been in my main roster for an entire year.
Then I got a bit snappish and said I don’t play games from companies that think I’m an idiot. Because while I learned this terminology from the fan wiki, I kinda always knew it.