In these days of "instant knife kills" in games, there are many things people don't realize. The first is that knife fighting is terrible, awful, gruesome, and absolutely vicious.
Often I've seen threads on various sites complaining about how the knife in tabletop game of so-and-so can't manage a one-hit-kill on anyone, particularly not in the hands of a near-untrained caster against a fighter. Some systems, like GURPS, make this slightly more viable (unlike things like D&D where at moderate level the knife will still do the same 1d4 damage it did at level 1 and the fighter will have 100 health), but the fact is that knives are kind of awful.
The other thing people seem to forget is that any critter that weighs half what you do can kill you. Humans, without conditioning and training, are freaking awful in a fight by comparison to the rest of everything. We min-maxed for IQ, and now we have things like guns. In a fight with nothing but fists and no technique to support their use? You wind up like this guy.
If you have good training and are in excellent condition, you can probably raise that number to your own weight, instead of half your weight. I use full-weight for myself, because I've invested significant time for fully 3/4 of my lifespan in my ability to fight, armed or unarmed. That's what it takes to be probably combat capable against things such as bambi, without the aid of tools.