the time in an activity when you cannot stop doing it but must continue to the end.

And although I was bored, I'd already spent so much time doing the research for the novel that I felt I'd reached the point of no return.

• knock spots off
• knock spots off someone
• knock spots off something
• knock the bottom out of
• knock the bottom out of something
• knock the daylights out of
• knock the daylights out of someone
• knock the living daylights out of
• knock the living daylights out of someone
• knock them dead
• knock the stuffing out of
• knock the stuffing out of someone
• knock the tar out of
• knock the tar out of someone
• knock up
• knock wood
• knock yourself out
• knock your socks off
• know-all
• know a thing or two
• know backwards
• know backwards and forwards
• know beans about
• know beans about something
• know best