Be bent on doing something

Context #1:

Jean: Phillip! I'm so tired! Can't we finish tomorrow? The project isn't due until 5 pm. We have plenty of time in the morning. Let's go to sleep!

Phillip: No way, Jean. I told myself we'd finish this by tonight and we're not going to bed until we do. Sorry!

Jean: You're being really selfish, you know. You're so bent on finishing this project but you're not considering any one else's feelings. I'm tempted to just let you finish it on your own.

Context #2:

Mother: Son, why are your grades so low in your science class this semester?

Son: I don't know mom. I work really hard but the teacher is bent on making my life miserable. She hates me.

Mother: Why do you think that? I'm sure it's not true.

Son: It's true. She doesn't treat me the same as others.

Mother: I'll have to go and talk to her then.

Son: NO! Don't do that. It's really OK!

Explanation: 

To be bent on doing something means that you are obsessed with doing something and you MUST do it.

In example 1, Phillip MUST finish his project, even if it means that Jean and he will lose sleep. 

In example 2, the son claims that his teacher is obsessed with making his life difficult. 

Be sure to change the be verb to match your tense and always use an ing-verb following on

She is bent on preparing all of the appetizers by herself. She won't consider a caterer. 

Mr. Lee has been bent on learning English in less than two years. He studies every single day. 

When I was a kid, I was bent on reading all of the Harry Potter books.

http://languagesystems.edu/

Bark up the wrong tree

Context #1 Alex: I'm sure that Cynthia took my candy. Mike: Cynthia? There's no way she took it. Alex: I think she did! She was at school yesterday. Mike: So was everyone else! It's a big school. Alex: She likes candy. Mike: Lots of people like candy. I think you're barking up the wrong tree. Alex: Wait a minute. Why are you so sure she didn't take it?

Context #2

Young Aaron's birthday is coming up soon. He will turn five years old on his birthday. Aaron's parents have been keeping Aaron's birthday present as a surprise but Aaron really wants to know what his present will be. As a result, Aaron is asking his mother all kinds of unusual questions to try to discover what his gift is. Aaron asks if his mother or father have gone shopping anywhere different. Aaron asks if his present is larger than a loaf of bread. He asks if his gift is hidden in the house. Aaron asks many questions. Finally, Aaron's mother says...

"Young man, if you think that I will tell you what your present is, you are very mistaken. You are barking up the wrong tree!"

Meaning: To make a wrong assumption about someone or something.

http://languagesystems.edu/