Why is it sometimes impossible to shut the trailer doors on sloped ground?

No you aren't.

Now I know you're trolling.

 

There was a scene in a movie, I think. I'm going to butcher it, but it was basically: "I can't think slow enough to understand what you're talking about."

 

How would you know it's not necessary unless you "fully understood this in terms of physics 100%"?

If you don't fully understand this in terms of physics 100%, as you have conceded, than you can not, by definition, know what variables are necessary in determining the calculation.

 

Free entertainment on a Sunday. Not even kidding. That's how I view you.

 

If it's such common sense than explain it to me like I'm a ten year old.

 

There you go. Now use that to answer the OP. Congratulations, learning has occurred.

 

And thus, we have a troll.

 

If the op took up carpentry...lol