Why Build From Source?

Question:

Why would anyone in their right mind build and install software from source code? (originally: I don't know why i build software without package managers.)

Answer:

1. Because you can customize it to your local requirements (AKA the Gentoo Lie)
2. Because security-wise it is more trustworthy than using packages (AKA the Security Excuse)
3. Because building from source makes you feel manly (AKA the BSD Delusion)
4. Because it isn't available in a package that will install cleanly on your system/platform (AKA the stability-vs-updates conflict, or New! vs Still Works Without Requiring Fixing!)
5. Because you can (AKA the Geek's Only Required Excuse)