There are four ways to "quit" something in Revit. The first and perhaps best way is to just pick another tool/command and do something else. Next (number two) is the ESC key on the keyboard. Sometimes you have to tap the ESC key twice to truly exit a command. Another (number three) is to use the Right Click > Cancel. This also may require using it twice in order to completely exit a command.
Last (number four) is the Modify button...on the Design Bar, the first one at the top of every Design Bar Tab.
Does the word Modify make you immediately think "Quit", "Stop", "Bail Out", "Escape", "Wait", "Let's not do anything now" etc? No? You are not alone. It is something that always puzzled me but I've never questioned, I just accepted it as "the way it is". Probably the best thing to do, but it remains a Reviteristic in my book!