As humans we are all fallible, because fallible means likely to make errors or fail. Nobody's perfect, after all.

Fall down on the job and you're fallible. It's a forgiving way to say you screwed up. If a scientific experiment's data is fallible, that means you can't trust the numbers. More than just locking your keys in the car, fallible can allude to a lack of moral strength. If in addition to locking your keys in the car, you kissed your best friend's husband, you might try using "I'm fallible" as your defense.