The feeling of dread as still a semi-junior sysadmin when an app doesn't work after an update.

I got stressed, triple-checked everything that I changed and that I followed all steps of the documentation of the upgrade process, then, as a last step before going over in half-panic mode to my boss, I try to restart the stupid java app and it starts working.

Wtf. Why. Why didn't it work the first time I started it? D: