For me personally it is very hard to watch scenes from movies/documentaries where the surgeon cuts patient's skin.
I don't get any discomfort from seeing blood or wounds but it's almost unbearable to watch as the doctor slowly cuts patient's skin with a scalpel (much less so if it's a quick motion).
Punctures (injections) are not that bad but still uncomfortable (weirdly, i did not feel any discomfort from watching the doctor take vein blood sample from my own arm).
I suppose there might be people who despite having similar discomfort might want to overcome it and become doctors. Do they have some training in medical school that helps them get used to these things? Or such people are simply seen an unfit for being a surgeon like if they for example had tremor?