There’s a whole history here – https://wordhistories.net/2017/12/18/work-cut-out-origin/
It actually apparently started out pretty neutral, like, you had your work set up and you had to do it. Wasn’t easy or hard work, just work. Then it started changing in meaning, to doing all the work you could take on. Then… yeah. Just kept changing.
A lot of people say it comes from tailors in the 1600s, where they would cut out pieces of fabric before getting to work on the real deal, but it seems like the original uses of the idiom never actually had a real connection to tailoring.
The meaning has warped, over time. That phrase is very old–like, way before the British colonies in America, let alone America, itself. It originally meant more along the lines of, “We have everything ready to being this project, so let’s get to work and do it.” Nowadays, it has a similar meaning–it’s still “time to get to work”–but it is generally used to imply a *lot* of work or very-hard work, as you noted.
The term most likely comes from tailoring, where you’d have Person A cutting out fabric pieces for Person B to sew together. When Person A has finished their job, Person B “has their work cut out for them.” Originally the phrase was just used to mean “We have work to do”, but it seems like over time it drifted to be used exclusively to imply particularly difficult work.
The literal origin dates back to the early industrial era when things were a mixture of automation and human labor.
Seamstresses and dressmakers used to have to plan out their designs, cut up the fabric, then stich it together. That took time, so clearly a person would only cut up and prepare the amount of raw fabric they needed to perform the next step. No sense in getting ahead of yourself.
Once industrialization came you could have a thousand unskilled laborers “cutting out” the designs from the raw fabric and then throwing them into a pile for the skilled seamstresses to sew and join together.
To have your “work cut out for you” meant you have a *huge* pile of work set out and ready for you, and you being the bottle neck to getting it done. You could equate to the modern day, “have my inbox filled with emails I have to reply to”. In short, you’re not waiting on anything, you’re not even waiting on a reasonable about of work, *all the work* is ready and waiting for your slow ass.
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