You can set your Mac so that if the mouse cursor is pushed into any of the four screen corners then a particular function activates, such as putting the Mac to sleep or activating Mission Control. This is called “Hot Corners” and can be activated by selecting Mission Control in System Preferences, then clicking the Hot Corners button and making a selection from the dropdown list.
What’s not at all obvious is that you can combine the Shift, Ctrl, Option (Alt) and Command keys with a Hot Corner so that pushing the mouse into a corner won’t do anything unless one of these keys is held down — useful for the not-so-rare occasions when the mouse can end up there.
Just press the relevant key(s) when the dropdown menu for the corner is visible. You can combine any or all of the modifier keys. The menu entry will change to show what modifier keys you’ve selected to use.