At school we had lots of BBC Micros. When I was near the start of school, these were very new indeed and almost none of the teachers or classroom helpers knew how to use them.
When you turned it on, you got a beep and a relatively unfriendly command prompt along the lines of:
To load and run the default program off a removable disk, they had a shortcut key combination: press shift+break to get that behaviour.
Easy, right? Except very few people understood instructions along the lines of "press shift and break together" to mean "depress shift and keep it depressed. Press and release Break quickly as if typing a letter. Release Shift".
So instead, minutes of pressing shift and break together, trying really hard to get them at the same time, would ensue at the start of each session until accidentally shift got pressed before the break.