What's the root cause?

KEY PHRASE
What's the root cause?
Investigating cause
A worried woman and a male coworker stand beside a laptop in a modern office, pointing at a frozen spreadsheet while office desks and papers sit around them.
Maria
The file keeps freezing when I try to save it.
David
I checked the network, and it seems stable.
Maria
What's the root cause? We need to solve it now.