For me it is not recording credentials with the assumption I would simply remember them later, while having every opportunity to archive them before eventually forgetting. Also, not keeping detailed enough notes & photos of exactly how my hardware is attached.
My payroll company came out with a be version that won’t work in Linux. They wouldn’t accommodate me and I was too deep into their ecosystem to change companies so I ended up having to buy a Windows license so I could run a virtual machine every time I had to do payroll.
Edit: My mistake was getting too dependent on a company that doesn’t care about Linux users.