How would you express "self defeating" in German?
Specifically, to express that someone is taking a perspective or actions that are actually leading him or her away from their goal instead of towards it?
A possibility to express "leading away from agoal instead of towards it" would be
"Self defeating" literally translated is "selbstzerstörerisch", but this would not express the mentioned meaning. "Kontraproduktiv" however expresses that the actions taken lead to the opposite goal.
Here are a couple of options:
sich selbst Steine in den Weg legen: Mit seinem Verhalten im Unterricht legt er sich selbst Steine in den Weg.
nicht zielführend sein: Dein ewiges Herumgediskutiere ist wirklich nicht zielführend! (Herumgediskutiere is obviously very colloquial.)
es sich nicht leicht machen: Du machst es dir aber auch nicht gerade leicht!
The Cambridge Dictionary says "self-defeating" is either
used to describe something that causes or makes worse the problem it was designed to avoid or solve.
or in American usage:
self-defeating — done in a way that keeps you from succeeding:
Even in German there are some more and very short alternatives to express this:
There is quite a long list to choose from, including from the other answers here.
Definition and example from wiktionary:
self-defeating (comparative more self-defeating, superlative most self-defeating)
Of a plan or action: containing elements that will cause it to fail; destined not to succeed by its very nature.
__ Cutting off your nose to spite your face is self-defeating.
Translation: Deine Nase abzuschneiden, um dein Gesicht zu ärgern, ist völlig [choose your poison from this page].
Or going with the Collins Definition of 'self-defeating'
A plan or action that is self-defeating is likely to cause problems or difficulties instead of producing useful results.
--> Ein Plan oder eine Aktion, die sich [choose again, this time I'd suggest: selbst schadet], kann Probleme oder Schwierigkeiten verursachen, anstatt nützliche Ergebnisse zu erzielen.
"Selbstschädigend" ist actually the nicest way to simulate official sounding German language usage.
For self-defeating prophecies the opposite of "selbsterfüllend" (self-fulfilling) appears to be "selbstzerstörend"1. The uses I found were all based on translations of Merton's essay from 1948 though (Merton, Robert K. (1948), "The Self Fulfilling Prophecy", Antioch Review, 8), and I'd say the term is not in general wide-spread use. "Selbsterfüllende Prophezeiung" is more common in non-academic contexts.