Think about it this way:
Every time you kill kbd, you generate a RANDOM number between 0-10000.
The winning number is always 1. (for example)
Remember that numbers you generate can repeat. So if you stepped on a crack you might get say number 1234 10000 times.
You have a 0.0001% chance of obtaining the item. Your chances never increase or decrease. You either get it or you don't.
Odds/probabilities only help you get an idea of how rare an event is. You may be confusing probability with ratio and proportion.