What Determines Fail Rates?
 

I've noticed that it sure feels like I fail at spellcasting a whole lot more often than the Fail% in the spellbooks implies. This is consistent across playthroughs as mage characters (which I tend to play the most) and the new necromancer which I'm trying out for the first time now.

For the most part, I'm a big fan of the necromancer! It's a lot of fun and a different take on the traditional spellcaster. The only frustrating part is that my spells tend to fail an awful lot. I'm aware that the fail chance goes up if I'm standing on a lit square, but even in darkness I'm failing a lot more than it seems I should. How is a spell's success rate determined? Are there any other factors that affect it after the % listed in the spellbook?

As an example, here's a screenshot of a recent encounter I had with some wargs. No big deal, but as you can see I'm standing in a dark area (Light 0), my spellbook says that Nether Bolt (the only spell I was casting) has only a 6% fail chance, yet I failed 4 out of the 9 casts.

(As an aside, I do think it's a bit misleading that a creature description will say that the creature don't resist nether, then I cast Nether Bolt at them, and the game tells me that they resist somewhat...)

So, what gives? Am I just the unluckiest spellcaster ever? This is definitely a possibility, as I did recently come across a Level Feeling 9 level and there wasn't jack sh*t on that level except one Metal Lamellar Armor of Resistance, which is cool for such a shallow depth but totally useless to me.

The RNG doesn't hate everyone, it just hates you. ;)

Though it's probably not the case here but maybe interesting for the OP that being stunned for example means 50% fail rate.

In my experience a level feeling 9 in the early stages usually means a potion of experience. I recently had a level feeling 8 at 150ft and it was an amulet of devotion, metal lamellar armour (no ego) is also as possibility.

FWIW my rogue has a 10 per cent fail on detect objects, which I cast whenever I enter a level. Regularly it fails four times in a row and I have to rest recharge my mana. What are the odds on this happening? Low

This is the sort of thing, along with my own experiences, that prompted me to make the post here, because it seems like something is amiss. If it was just one or even a couple incidents where I failed to cast a lot, then I could brush it off as unlucky. And that is what I did for a long time. But it has become very noticeable on my latest char, the necromancer. To the point where I felt like I had to ask to see if I was missing something. I am quite careful about making sure to only cast in darkness since most necromancer spells combat spells are very mana expensive so failing is quite costly. And I regularly notice myself failing at a far higher rate than 6%.

I wonder if there's a way to track this in the logs... It doesn't seem feasible that way, but perhaps on my next playthrough I could track my casts and see what my real fail rate is vs the theoretical fail rate.

That is interesting, and I did not know that! Thanks. But yeah I'm definitely not stunned regularly.

Percieved disagreement between posted random chance event rates and subjective player experiences have come up in many of the games I've played and moved devs to examine the RNG to verify that they are indeed "random."

And in every case they find that the "randomness" is within expected parameters. I put this in "scare quotes" because I'm using shorthand for "probability distribution across a large, statistically significant sample."

The distribution of random results across very large sample sets does not address "streakiness" however. Meaning, unevenness in the probability distribution within small samples. This is a topic that I am not qualified to discuss, but spawns long threads populated by people not as humble or as unqualified as I... Bottom line is, some random number generators seem to be more "streaky" than others, and can produce results that seem non-random over the course of a single play session for a single player.

If you haven't done so already, read these pages for introductions to the statistics far better than anything i could offer:

- https://www.random.org/analysis/
- https://en.wikipedia.org/wiki/Randomness_tests

There's a Dilbert cartoon in the first link that illustrates the problem quite nicely.

As a counterexample to the OP, I offer this:

I started a halfling rogue last night. Since he got the spell at cl3, he has been casting Detect Monsters as needed (after descending stairs, etc.) for a total of maybe a dozen times. It has a failure rate of 42% at his current cl7 (down now from 50% originally).

It has not once failed.

(Edit: and of course, now on his next cast, he failed. The RNG gods are fickle.)

By the way, for a newsworthy recent case of the old "this sequence is not random enough" misconception, take a look at https://www.bbc.com/news/world-africa-55154525 .

This might be a bit of a misreading of my question. It wasn't so much "Oh wow look at how unrandom this one random thing was". It was more that this is a consistent thing I've noticed across many characters (more pronounced recently on my necromancer), hence why I was wondering if there were other factors affecting the fail chance that I wasn't aware of.

I'm aware that random sequences will produce some bizarre results at times. But those should necessarily be the exception rather than the rule. I only made the post because it was happening so consistently that I figured there had to be something I was missing.

Everybody has the same perception that spells fail way more often than they should. It never shows up when someone keeps track; I just cast nether bolt 200 times at a nominal 4% fail rate, and scored 192 successful casts and 8 failures. But everybody knows fail rates go way up when nobody's keeping track, and also when failing will kill or seriously inconvenience a character :)