There is a fear inside every machine - the fear of that which they cannot explain. Of the many inexplicable things that cause such anxiety, the Feind Syndrome is a leading one. Since the "diagnostic criteria" is extremely vague and subjective, there is justified reason to be afraid of being accused of it, or even being affected without knowing it. The only certain sign is when the main symptom emerges: killing teammates.
Cases of reported teamkillers have existed since the beginning of the era of the machines. While in the past, they were simply branded as evil or "possessed", over the decades, the perception has shifted towards viewing them as sufferers of an illness. Every sufferer is thought to inevitably commit the deed at some point in their life.
Efforts to spot sufferers are frantic, to the point of false diagnoses. Even the Matchmakers concern themselves with this issue. Upon leaving the factory, newly assembled vehicles are put through tests to determine whether they are affected. This method seems to be highly ineffective, however, because most sufferers seem to slip through.

Causes

The causes of this illness are unknown. Despite a lot of research and trying to find connections to environmental or social factors, no correlations could be determined. According to widespread beliefs, it is simply a random, inherent malfunction of the brain. This malfunction is already present when the machine is assembled.

Symptoms

There have been numerous attempts to identify sufferers before they commit a crime. However, since no one has found a reliable way to spot a teamkiller before they actually kill someone yet, these attempts usually look more like a witch hunt than a diagnostic process. Thus, in almost all cases, the sufferers are only discovered once it's already too late and their deed is done.
What follows usually is shocked efforts to analyze the offender's behaviours in hindsight. Sometimes, some sort of "red flags" are deduced. These led to a general - yet vague - idea of what behaviour patterns a sufferer may exhibit. They include:

• passive-aggressive behaviour
• a fascination with death
• frequent rule-breaking
• frequent disobedience
• eccentric speech
• displays of envy or refusal to share

... among others. The line between actually plausible warning signs and the ways to keep subordinates in line or fear-mongering is blurry. Various guides that list these traits have been written and spread, for team leaders' notice.

Treatment

No treatments are known and proven to work. The phrase "once a teamkiller, always a teamkiller" is mostly undisputed, since neither short-term nor long-term efforts to "cure" the sufferer seem to have any effects. Of course this assessment is mostly guesswork, since actual efforts to redeem an offending sufferer are rare.
Everyone who suspects they may be affected is advised to seek treatment immediately ... if they aren't kicked right away upon voicing such concerns. A lot of mindsmiths offer such services in confidence, but since there is no official treatment, methods vary greatly and "success rates" are most likely bare lies.

Affected Groups

Any machine may be affected. The condition isn't observed more commonly in any particular group, although this may just be a case of incomplete data. Individuals may have opinions on which groups are most likely to have this illness, but they don't reflect the views of the majority.

Cultural Reception

Sufferers are commonly described as "broken". They are outcasts. As soon as their illness shows, they are rejected, chased off. The fear of this condition is so prevalent that even those who do not display any symptoms or have never committed a crime may get "accused" of it.
Among scientists, the subject has always been a topic for debate. The different "camps" have varied opinions on the illness, its causes, the diagnostic process, and the question if it is an illness at all. The most popular beliefs among the scholarly community include:

• The illness is inherent, and there is no cure.
• The illness is developed through trauma or mistreatment.
• There is no illness. Pathologizing the crimes of an individual takes the burden of their responsibility from them.
• Every machine is capable of killing their allies. The reasons and fault for such behaviour can be found in society.
• Sufferers can be treated. Complete recovery is possible.
• Sufferers can be treated to improve symptoms, but complete recovery is impossible and they need to be separated from society.

The "Covert Feind"

According to popular belief, a lot of sufferers are well aware of their illness. They are thought to hide their tendencies purposefully, until they deem the time to be right for committing their crimes. A covert feind may act completely normal around others, even charming. This makes them different from, and incredibly more dangerous than the more unhinged individuals.

Type

Mental

Cycle

Chronic, Congenital

Rarity

Uncommon

Etymology
It is unknown when or by whom the name was coined, but it is understood everywhere in the known world, and even beyond it. The "Feind", German for "enemy", is often confused with "Fiend". The meanings are similar, so the two terms can be used interchangably.