I went on a business trip once to Utrecht in The Netherlands.
Got the 0600 flight from Dublin, so was up at 0430.
It was a long day of meetings: I was shattered when I got to the hotel restaurant for dinner at around 1830 (Dutch time; 1930 Dublin time).
As I waited for my order, I picked up one of those small rolls of bread, and a butter knife. I began to cut through the bread with the knife. The butter knife. I continued cutting through the bread with the butter knife. I cut through the bread with the butter knife.
But I forgot to stop cutting. It wasn't until I had caused myself grievous bodily harm (in the palm of my left hand) when I stopped cutting.
With the butter knife.
It wasn't all that painful at the time, and I had no other problem eating my dinner, going up to my room, and crashing until my phone woke me up the following morning.
For the next 4 days, though, it was agony. Every flex of my left hand brought that horrible feeling that I was going to open the cut again.
Now. Picture that fantasy movie or pseudo-historical TV series where the hero kneels in front of the shrine, raises his arms in supplication, and prays that if he prevails in the forth-coming trial/battle/ordeal, he will sacrifice a dove, or a bull, or his mother-in-law to the god right in front of him (or any other god who happens to be ear-wigging at the moment, for that matter).
Then he pulls out his dirk and seals the deal with blood by slicing the palm of his (isn't it always) left hand, and letting it bleed on the alter.
Finally, he takes out a grubby, probably-infection-ridden rag from his pocket and wraps it around his hand. He stands, smiles at his buddy, claps him on the back, and they head off to the nearest brothel for a just-in-case last shag.
Picture him later in the show. Is he wincing because someone bumped on against his left hand? Does he run in trouble in the fight because he can't swap his sword to his other hand to get a better reach at the careless and reckless enemy fighter?
Well, I can tell you for sure that this is not how it would happen. He would be in pain the following day, and agony the day after. He would spend the whole fight nursing his left hand up by his chest for fear that he would have to use it.
He'd die a gruesome death at the hand of a 13-year-old, drafted in to the enemy horde because all the able-bodied men are already dead. It would be a shameful death, but fair, because the gods despise idiots.
At least he got that one-last-shag, though.