I'm looking for a word that would describe a phenomenon of noticing things only when they go wrong. "A thing that's only noticeable when it goes wrong is ... "
I think there are more basic answers with the connotations the asker is going for. Such a thing is "taken for granted" (phrase used in Kat's comment) or treated as a "given". If you are responsible for providing it, you have a "thankless job" -- you do essential work in the background and will get more attention for the one time it goes wrong than the thousand times you do the job right.
When something has always worked to the point that a breakdown is inconceivable and yet happens, that is a "black swan".
I think I know the kind of thing you are talking about. For instance, in film production, things like focus and keeping the microphone out of the scene are only noticeable if they go wrong. When you drive, you only really think about your brakes if they don't do as you expect.
But, if that's what you mean, then I don't think there is a word in English for it. The concept comes up often enough that variations on the description "that's the sort of thing that you only notice when it doesn't work" is one I've come across a number of times. So, if there is such a word, I don't think very many people know it.
To borrow a term from organizational theory: hygiene factor
A hygiene factor is a something that does not generally contribute to satisfaction when present, but causes dissatisfaction when absent. Having good hygiene doesn't make a person more likable, but having bad hygiene would make others have a negative opinion of the person.
If you can use a twist on an idiom, I think an unsqueaky (or quiet) wheel would work well for this.
The traditional saying is
The squeaky wheel gets the grease/oil
Following this meaning, a wheel which doesn't squeak (isn't causing a problem) is not going to attract attention.
A couple of examples of the phrase used this way:
[T]here is a strong tendency [for decision makers to focus on] the steps that are known from the outset to be fraught with danger, the "squeaky wheels." Consequently, they tend to overlook the more subtle or hidden risks in any relatively nondangerous or routine step in the plan. This is what I refer to as "the unsqueaky wheel trap." —Irving Lester Janis, article in Information Systems: Failure Analysis, John Wise & Antony Debons, ed., 2012
I suspected the Unsqueaky Wheel hadn't gotten enough oil. Being undemanding in a hectic home, she was easily overlooked —Judith Ruskay Rabinor, A Starving Madness: Tales of Hunger, Hope, and Healing in Psychotherapy, 2013
You question specifically asks for a term that stands for two failures, one of which remains hidden until the other's failure. There are a few terms from specific disciplines that do this.
In genetics, its an "unexpressed" or "suppressed" gene. The unexpressed gene lacks an unlocking enzyme not normally present, while the suppressed gene stays turned off in the absence of a normally occurring blocking enzyme. When a genetic error elsewhere makes the unlocking enzyme or fails to make the blocking enzyme, we get an abnormality.
In espionage, its called a "sleeper cell."
In software, its called a "Time Bomb" or "Logic Bomb" virus, if deliberately placed, or a "conditional capture" if its an undetected mistake not found during normal program operations.
In statistics, its sample "covariance", which drastically reduces the true power of multi-variable correlations.
In systems diagnostics, its a "cascading failure".
I like "latent" as the expression of an inherent, perhaps unknown, failure mode; but, it doesn't automatically imply that something abnormal must occur before it comes to light. Any of the discipline specific terms up indicate the dual, dependent nature of the failures.
The closest I can come to this meaning is "oversight", which actually has several meanings:
- watchful and responsible care, regulatory supervision
- an inadvertent omission or error.
The company claimed the accounting error was simple oversight, but the prosecutor countered that it actually counted as criminal negligence.
Because none of the committee was directly responsible for managing the investigation, its failure was due more to oversight than incompetence.
I've called the types of devices which are noticeable only when they fail as "spleens".
The spleen is an organ found in mammals and reptiles whose operation is completely unnoticeable so long as it is healthy, few people even know its function even if they know its name. However, damaged or diseased spleens are very painful and very dangerous.
This is not a well-known usage of the word but I've found that people understand it easily.