Quick answer: Oops Surgeon counts surgeon's errors: failed attempts to remove, add or change an organ. You need 25 in total for all six levels. The trouble is that high Anatomy mastery (especially with the Expert Anatomist perk) makes failing rare. To fail on purpose, take your tools off and work on organs that need high mastery (11 or more). Players also got it by swapping organs on zombies: a failed swap counts too.

Players ask cannot get Oops Surgeon inspiration and is it even possible to mess up organ extraction. It is; you just need a job harder than your mastery.

Quick facts

  • Counts: failed organ removal, adding or changing (skin, bones, skull, heart, brain, guts)
  • Total needed: 25 errors for all six levels
  • Faith to claim: 23 in total (level I is free)
  • Hardest part: high mastery makes errors rare
  • Easiest source: hard organ swaps on zombies, with no tools

Levels

LevelErrors in totalFaith
I1free
II31
III72
IV104
V156
VI2510

How to fail on purpose

Unequip your tools

Tools add mastery. Take them off before you cut.

Pick organs that need high mastery

Gold-star organs can need 11 or more. The bigger the gap between the requirement and your mastery, the likelier a fail.

Swap organs on zombies

Changing a zombie's organ is surgery too, and a failed swap counts. Repeat on the best organs you have.

If you haven't specced into Anatomy yet, farm the errors first. Every mastery point you add later makes them harder to get.

Related

  • Zombies: raising zombies and the organs they need
  • Faith: where the Faith to claim each level comes from
  • Guide: every answer in one place

Sources: a Steam General Discussions thread on Oops Surgeon, wikily.gg.