Feuerfest

Two-Factor authentication is a fine feature. Just not when you must wipe your entire device and don't have a proper backup of the enrolment QR-Codes and secrets..

Always keep track to which repository you are committing...

Never work for a company that opposes unions.

There are a bunch of websites and Youtube videos trying to tell you that the locally installable Microsoft Office versions can be downloaded, legally, free of charge, directly from Microsoft. This, of course, is nonsense.

I rarely have to use SetEnvIf manually in Apache2. But when I have to use it I'm always amazed by its capabilities.

Using ICMP to monitor if a system is working is not a good idea as CPU Soft Lockups do exist.