Sometime, it’s very hard to understand understanding.
Sometime, it’s very tiring to understand.
Sometime, it’s much more complicated than programming
Sometime, it’s very hard to debug
Sometime, you can’t even find the bugs
Sometime, log files didn’t show you the error message
Sometime, you want to reboot
Sometime, you want to hibernate
In most time, you do not want it hang

Relationship, it’s hard to monitor and maintain