You put the ingredients in, the bar filled, the craft finished, and the window handed back nothing at all. The craft did exactly what it was built to do.
Thirty recipes in Graveyard Keeper 2 are graded rather than made, and a graded recipe is the only kind the game will let you start when you are not good enough to finish it.
Which recipes are graded, and why they let you in
Every prayer at the 
Writing Desk is one, along with the 
Story, the 
Newspaper and the 
Written Hardcover Book. The four embalming fluids at the 
Formulation Bench are graded too, and so are the 
Bowl of sauerkraut and the 
vegetable salad at the kitchen table.
Every other bench in the game checks your mastery against the requirement and stops there. The button prints your number over the one it wants and nothing happens when you press it.
A graded recipe skips that check on purpose. The button lights at any mastery, the craft runs, and the shortfall is settled at the end instead.
Every swing is a coin flip, and a miss still costs a tick
Below the requirement each swing has a chance to count equal to your mastery divided by what the recipe asks. Half the required mastery is a coin flip per swing, a quarter of it is one swing in four.
A miss does not cost you a retry. It burns the tick anyway, so the craft always ends after exactly as many swings as its duration and the only question is how many of them landed.
Under bronze, the output list comes back empty
The successes are counted at the end and compared against three numbers. Clear the gold line and it is three stars, silver two, bronze one. Finish below bronze and the grade is zero.
The ingredients are gone, the time is gone, and the output is an empty list. Nothing on screen says what happened, which is why this reads as a bug the first time it bites.
The technology points are paid anyway, because the reward is handed over before the empty output is dealt with. A failed craft still moves the tree along.
What the odds come to
A Written Hardcover Book is the worst of them. It wants four in Book writing and needs five successes out of fourteen swings, so at mastery one it comes back empty 73 percent of the time.
Raise that one point and the same craft fails 8 percent of the time. Take it to three and it never fails at all. One point of mastery is the difference between losing three quarters of your materials and losing none.
A Basic Prayer needs one success in twelve swings, so it fails 7 percent of the time at mastery one. It is the one to learn on and the reason the system stays invisible for so long.
Prayer for Repose needs four in sixteen and fails 88 percent of the time at mastery one. The Hypno Prayer fails 99 percent at one and is still failing four times in ten at mastery four.
Embalming sits in between. A 
Solution for Corpses or an 
Injection for Zombies wants six in Anatomy and needs one success in eight swings, which comes back empty a quarter of the time at mastery one.
At the requirement, everything is gold
Reach the number the recipe asks for and the rolling stops. Every swing lands from then on, which means the successes always reach the gold line, on all thirty of them.
So the grade is binary rather than a gradient. There is no reason to push mastery past the requirement for quality, because the requirement already gives you the best version.
Put a zombie at the bench on one and its mastery is raised to the requirement before anything is rolled, so it never misses and never fails. A poorly trained zombie makes three star books you could not make by hand.
What you give up is throughput and the choice of recipe, so the sensible split is to hand a zombie the graded work and keep the rest yourself.
Graveyard Keeper 2 star crafts FAQ
Why did my craft produce nothing in Graveyard Keeper 2?
It was a graded recipe and you finished below its bronze line. The grade came out zero and a zero grade returns an empty output, with the ingredients already spent.
Which recipes can fail like that?
Thirty of them: every prayer, the Story, the newspapers, the Written Hardcover Book, the four embalming fluids and the two star dishes at the kitchen table. Everything else refuses to start instead.
How is the chance calculated?
Each swing counts with a chance equal to your mastery divided by the requirement, and a miss still spends the tick. The craft ends after its duration either way.
Does a failed craft still give technology points?
Yes. The points are awarded before the empty output is handled, so a craft that produces nothing still pays its red, green and blue.
Is it worth raising mastery past the requirement?
Not for quality. At the requirement every swing lands and the result is always three stars, so pushing higher only makes the craft faster.
Why do my zombies never fail these?
A zombie has its mastery raised to the requirement before the roll, so it cannot miss. Give a zombie the graded recipes and it will hand back three star work at any training level.
