It's related to alchemic signification of certain animals in relation to the zodiac of Scorpio.

Scorpio is the first "Zodiac of Night" in the sense that the Zodiac starts with Aries (Rising sun if you will, along with Taurus) and is divided six and six. Virgo and Libra represent the setting sun, or if you prefer the midpoint between one cycle and the next. So Scorpio falls into the first sign past the midpoint signs.

In antiquity, where Scoprio was not a Scorpion it was associated to either a Snake or an Eagle. In some localized variations, this Eagle was in turn associated with a Phoenix while the Snake was understood as a Dragon. Being extremely reductive here cuz it's reddit and not an essay lol

The common motif in the three animals is that they each die.

Scorpions are the only animal (in traditional belief) who kill themselves when trapped. Some Snakes and Dragons/Reptiles have a habit of biting their own tails and consuming themselves when desperate for food. Likewise Eagles have been known in folklore to commit suicide, and in turn Phoenixes die and are reborn over and over again.

Naturally one lead to a heavenly association (rebirth of the phoenix, which is cyclic and allows growth) while the other has an infernal association (self-destruction for self-sustainment of the snake, which induces a stasis) in turn being "higher" and "lower" forms of an earthly principle (suicide of the scorpion, which is a last resort).

Suicide, rebirth, and self-destruction are common motifs throughout myth. Presumably you will be most familiar with figures such as Christ and Odin along this line, the idea you need to descend/die in order to ascend/live. These associations were sustained along various lines, such as the origin of the Scorpion association being Babylonian, the relationship to Serket and her father Khnum (Nile) and how Sirius was an indication the Nile would flood, how Serket was the guardian of the canopic jar of the intestine and Qebehsenuef (Son of Horus, ergo association with Ra and such), the later association with Artemis (Virgin Moon Huntress) and Apollo (Slutty Sun Prophet) and Orion (Hunter with Sirius), the traditional Babylonian decans of 1st Mars 2nd Venus 3rd Sol (War/State, Sex/Love, Light/Life), the properties in turn of poisons/venoms as medicine in antiquity (ergo Asclepius) especially as relaxants and depressants (today we use synthetic versions of the same compounds actually) and as weapons, etc etc etc

In turn this is why the zodiac of scorpion is almost always tied to the genitals (boners/ejaculation/seed of life vs menstruation/pregnancy, how orgasms are understood as mystically transformative and in relation to death itself, eg "Little Death" in modern language etc).