The Drunken Lizard Pub

When trying to picklock a chest with a chance of 25 %, normally you should succeed in about 4 times.
But sometimes, I need 8 tries. Why?
Are the displayed 25% the chances under normal conditions. Do I have a malus plus, if the room is too dark.
Or do the 25 % mean, that a lock of this type is usually opened with 4 tries, but you can be lucky to open it in one try or be unlucky to open it in 8 tries?

... and if you have 0% chance to open it (the chest at Liliths house):
Do you never have the chance to open it, or if you are very very lucky, you could open it nevertheless?

Joe, it is just that a 1 in 4 chance. That does not mean you will succeed in 4 tries. If you have a 4 sided die and you roll it 4 times it may not roll a 1 any of those times. But it has a chance that it will. Same thing with locks. Think of it like calling heads/tails on a coin each time you throw it. You won't be right everytime, but have a 50/50 chance to be right.

Specifically if the chance really is 25%, you have about a 68.36% chance of succeeding at least once in four tries. The rest of the time, you'll fail.

Thanks for the explanation.
@Slarty:
First I was confused about the 68.36%.
Then I started to think about it, calculated it and got the same result!
Yes, now I really understand it