Learn Hardcore Korean: yeonghwaga junggane neomu jiruhaeseo nawasseo. - The movie was so boring in the middle that I left.

In Korean, -가 and -는 are subject markers, while -를/을 mark the object. Here 영화가 indicates that “the movie” is the subject being described as boring. You’re not doing something to the movie (so it’s not the object); rather, the movie itself is the one causing you to leave.

What does 중간에 mean and why is -에 used?

중간 means “middle,” and adding -에 turns it into an adverbial meaning “in the middle (of it).” So 중간에 means “during the middle part.” You use -에 with time expressions to say “at/in that time,” whereas -에서 would suggest a location where an action occurs (“at a physical place”) and is not used for “during.”

Could you say 중간에서 instead of 중간에?

No—중간에서 would imply an action happening at a physical “middle spot,” which sounds odd for a time reference. When you want to say “in the middle of [something],” the correct marker is -에 (as in 수업 중간에, “in the middle of class”).

Why is 너무 placed before 지루해서? Can it be left out?

너무 means “too” or “very.” Placing it before 지루해서 intensifies the boredom: “It was way too boring.” You can drop it—영화가 중간에 지루해서 나왔어 still works—but with 너무, you convey stronger frustration or annoyance.

Why do we use 지루해서 (the -아서/어서 form) instead of simply 지루했어?

The -아서/어서 ending connects two clauses, showing cause and effect: “because it was boring, I left.” If you said 지루했어, you’d just state “it was boring” without explicitly linking it to your action of leaving. So 지루해서 나왔어 = “it was boring, so I came out (left).”

What nuance does 나왔어 carry here versus 나갔어?

Both come from “to go out,” but 나왔어 is from the perspective of someone inside: “I exited to the outside.” You’re speaking as if you were in the theater and then “came out.” 나갔어 is from an outside viewpoint: “They went out.” Since you’re talking about your own movement from inside the cinema, 나왔어 is more natural.

Why isn’t there a pronoun like 나 or 저 in this sentence?

Korean often omits the subject when it’s clear from context. Here, it’s obvious that you are the one who left, so there’s no need to say 나(는) or 저(는). Leaving it out makes the sentence more natural and less redundant.

How would you say this sentence politely?

You can simply change the ending to polite style:
영화가 중간에 너무 지루해서 나왔어요.
Or even more formal:
영화가 중간에 너무 지루해서 나왔습니다.