Rust:

• You find a predefined foot shooting function, but it’s marked as unsafe and someone forgot to document what the safety contract was. You write up an unsafe block anyway and pass that function ownership of a bullet and a mutable reference to your foot, and get a segfault.
• You search crates.io for “gun” and find a crate called pewpew. It looks incredibly spiffy. It supports semi or automatic fire, being used with or without a turret (or on a user-supplied turret) and with any number of middlewares for storing the bullets and transforming them on their way to the firing chamber. Unfortunately you can’t shoot yourself with it because your foot doesn’t implement the relevant autotraits.

Systemd:

• You create a service file for shooting yourself in the foot and set it to run at system startup. It seems to work, but after a cold boot, sometimes your foot has a hole in it and sometimes it doesn’t. After hours of debugging, you discover that this is because sometimes the gun service starts up and fires its bullet at nothing before the foot service finishes initializing and puts itself in the way. To resolve this you will likely need to edit the source code of your foot to make it support systemd-notify.