Anyone who has studied a second or third language knows that prepositions are killers. They usually cannot be directly translated, and there are multiple meanings for each one in every language. Just think for a moment how many different usages there are for the preposition "up" in English.
look up (and even that has several meanings!)
A few days ago I was talking to a German friend of mine and telling her about another friend asking me to fill in for her with our volunteer work because she had an unexpected conflict. I was explaining to Friend 1 why I had shown up instead of Friend 2.
So here's what I said along with the translation:
"Sie hat mich gefragt, ob ich einspringen könnte weil sie zum Arzt gehen musste, und...na ja, ich hatte nichts an, also warum nicht?"
"She asked if I could fill in for her because she had to go to the doctor, and since I had nothing on, there was no reason I couldn't help out."
Right. What I meant to say was "Ich hatte nichts vor," which would have meant I had nothing going on.
The worst part was that I heard and recognized the mistake as it was coming out of my mouth - kind of like how you see a glass vase falling in slow motion as you make several desperate attempts to grab it on its (seemingly) 5-minute fall to the unforgiving floor. "Nooooooooooo!"
These teeny tiny little words have such tremendous power...
I've been learning, studying, speaking, hearing, reading, and trying to improve (my) German for 33 years, and this shit still happens to me. At least they make for fun stories.