Ask HN: What was the most important technical invention of humanity?

The Flux Capacitor

Fire. That's something of a cliché answer, so here's my reasoning:

First of all, you probably don't interact with a bare fire on a daily basis. Most of the functions that fire used to serve have been replaced by electricity based solutions.

The heat of fire is a cheap and easy (compared to waiting for a lightning bolt to hit) way to cook food. Cooking of course opens a lot of possibilities in the realm of what's edible. How often do you eat raw meat?

Fire can be used to heat spaces, allowing people to live where it's cold.

Fire let's you light up dark spaces, it's a primitive sort of night vision.

Fire wards off predators, making it safer to sleep at night. (There was a time when large animals dangerous to humans weren't nearly extinct.)

Fire is a decent tool for clearing land.

Fire is used as part of a key step in tons of early manufacturing processes, including smoking foods, brewing alcohol, etc. (Both of those are methods of preserving foods that are cheaper than using salt. Which you can get by boiling sea water, to add another use.)

But really, that's just the tip of the iceberg. In addition to all of those things, Fire was (to my knowledge) the only way to generate enough heat to smelt ore, a process that should require no explanation as to its importance.

Depends of the definition of "technical" as well. If taken to mean anything that humans create, including replicating natural processes, then as other posters have said fire is the obvious choice. Now if you restrict technical to purely man-made devices it does get a bit more difficult.

soap

Probably language, the ultimate force multiplier. Followed by the wheel.