Been there
Conversation with a usually competent colleague:
Him: I can't import this certificate
Me: Oh really? Let's have a look...
[Quick screen share]
Me: Right, so what you've got isn't cert.crt, it's cert.crt.txt, turn on your bloody file extensions
Him: D'oh, thanks, sorry Outski and rest of the team whose time I've wasted
----> one of many beers owed by the left pondian team for dumbass mistakes