As I've said before,the trial and error aspect of the game is a fundamental mechanic of roguelikes.
Take Binding of Isaac for instance. You would probably lose to a boss you'd never fought before ten billion times before you figure it out. At least you're expected to lose several times before you begin to understand its strengths and weaknesses.
Darkest Dungeon, being a roguelike is no different. The problem is that you can't just start a fresh run if you lose to a boss in this game. It's much more grindy and frustrating when you have a party wipe. So if you don't want that to happen,you can lower your chances by researching it first.
There's a HUGE difference though between this game, and somethign like Isaac, or any other.
Let's look at Starward for example, and because I'm lazy and it's the easiest for me to explain. Yes, you're likely to lose to a new boss; they're made to kill you after all. BUT. You WONT lose JUST because you dont have the tools to beat them. Even against a boss you have never fought, you DO have the tools (I make absolutely freaking certain of it), and knowledge, to beat them. Bosses in that game attack with patterns that are typically made of slow-moving bullets; you have time to analyze what's happening on screen, and figure out a way to dodge it, or otherwise deal with it. The patterns are also layered, as a rule, each pattern being made up of multiple layers given specific colors to make them easy to pick out, so that you can see, that much easier, exactly what's happening. Through it's visuals, the game is giving you all the info you need; if you are good enough, you can win the FIRST time.
But if Starward worked similarly to DD (aka, NOT giving you enough info), it'd work like this: Bosses using hyper-fast attacks requiring you to have memorized, IN ADVANCE, where to stand and what's going to happen in order to not get hit. You're just not given visual info in that case. You DO NOT have the tools to win the first time. It becomes, in essence, trial and error, even if you're very skilled at the genre. Some traditional shmups do this, and I tell ya, they aint much fun.
Isaac is similar to Starward in this way. Enemies dont use hyper-fast "need to be memorized" moves against you. Bosses tend to have very visible tells, bullets tend to be slow-ish, and even when they do something new, it's usually shown in a way that's pretty obvious as to what's likely to happen. For instance if you see a boss (like Monstro for instance) suddenly launch into the stratosphere, the pretty-darn-obvious conclusion is that some sort of big downward stomp attack is coming, because what goes up must come down. With ten kersquillion bosses the game does make a few mistakes here (such as Conquest's hyper-RNG light beam attack, or the Heart's spinning brimstone attack) but for the most part the bosses, and the enemies, always follow these rules. You have the info, visually, to take them down the FIRST time, even with a bad build, if you're good enough.
It's all alot like that Dark Souls example I'd given before.
And giving the player that info... regardless of the type of info... is important. Even most turn-based roguelikes (the GOOD ones, anyway) do this. Usually you can check new enemies/bosses to see info on them and what they can do, so that you can start planning on how to deal with them with your current build/inventory. Yeah, some roguelikes get this horribly wrong of course, but again, the truly good ones generally get it right.
It really is an important concept in game design as a whole. When it's missing, the whole game suffers, regardless of which game it is.
