Break a Leg

Wikipedia says:

Traditional Theory

In the United Kingdom, the most common idea about the origin of the expression comes from tradition. Historians know from the time of King James I and Shakespeare's King's Men that actors would, on occasion receive tips on top of their salaries. Rather than receiving tips directly from the company or theatre, tipping was left to the audience. During the final bows or curtain call, audiences would throw money, usually coins, onto the stage depending on how well they enjoyed the performance. In some bad performances they would throw rotten vegetables, but in the good cases, money. Actors would then 'take a knee', effectively breaking their leg line, on stage and pick up the money. As a result, when a person wishes someone to 'break a leg' it refers to wishing them success in their performance so in the end they would have to kneel down and collect a welcoming tip. Theatre evolved and the tradition of tipping changed to one of throwing flowers on stage, as well as presenting flowers.

Antonym Theory

Breaking one's leg is not a good thing to hope for - therefore - by some superstition - if "good luck" causes bad luck, then the perceived bad luck of breaking one's leg causes good.

******

Whatever the theory may be, "break a leg" is closely tied to the theatre stage for good reason.
On opening night, after the curtain call, I hit my knees on a bench in the dark and fell over. Owwww....
Saturday night, I kept a wary eye out for the bench but tripped over a power cord on a blackout entrance after the break was over.

Sunday afternoon, I managed to stay whole but 2 cast members went missing so the rest of the team healed the gaps, re-choreographed the vital elements and pulled the scenes off beautifully.
There were pops and bumps but the play moved forward, as things do when there is love and unity in the company.

One weekend down, another to go!