Until the directory structure and filename, including your SharePoint hostname, exceeds 400 characters and then it just breaks. Because, Microsoft.
Surprisingly easy to do with some quite nested folders with spaces in the names (as that takes 3 characters per space) and a long filename.
Wait until Corporate sees the new data storage rates for 365 for next year and their potential new bill for cloud storage.
They'll be spinning up those server room file servers in no time.