You cannot wield a combat knife with one arm

Like, okay, you could make a case for that, but I was actually trying to find a way to kill myself explicitly here, so in my roleplaying mind it didn’t make sense.

I will say that the message could be a bit more clear in cases like this. Your strength is currently too low to hold it with only one hand. Unless a weapon is tagged with a specific flag (ALWAYS_TWOHAND), the game will determine whether or not it takes two hands to use based on the item’s weight/volume versus your current strength. Since combat knives do not have that flag, they can be either one or two handed weapons, depending on your current strength stat.

Ah, that makes sense.