It's not that it necessarily sounds stupid, people express emotions straight up, especially extreme ones (ie. I hate you! I love you.) However, a common mistake screenwriters make is to have characters express there thoughts directly. In most cases, this leads to boring dialogue with no subtext to it.
Below is a scene which is "on the nose". Following is the same dialogue courtesy of Tarantino. (I just grabbed a random bit of text, it's most certainly not the best example.)
ON THE NOSE:
Don't worry about me. I'll take your car. I'll be back soon.
I have to go. Can you trust that I'll return shortly?
I trust you.
Here's some money. Go on, get those pancakes, have a nice breakfast. I'll take your Honda. Be back before you can say "blueberry pie".
Maybe not that fast. But pretty fast, okay?
No, granted, I'm reading into the "okay"'s in an actor sort of interpretation. It's not like that part is particularly profound. However, more to the point, is the first set of dialogue and how clunky it is. And actor could bring that dialogue to life, but it in the end will not be interesting to the listener. Again, I'm sure I could have grabbed some dialogue with better subtext, but well, I've got to get back to my writing.
Hope this helped.
Pulp Fiction - by Quentin Tarantino
Me and my own writing knowledge....whatever that may be...