The entropy of the system increases over time
Disk space will overflow with logs, other misc data
Memory leaks, however small will eat all the memory over time
security vulnerabilities are discovered
hardware decays/breaks
dependencies change
partial updates of the system are hard
the update while maintaining the uptime is hard
network will go down/do weird things
Install security updates
Security configuration in general
Backups
Be careful around state management
Careful around making any changes
And this is all assuming hardware is an abstraction (e.g. you're using cloud VMs) which is far less true if you need something to exist over time
I have a bit of a hosted infrastructure PTSD from my time working at Amazon 😅