“iseongeul aesseo nulleo” most likely means “trying hard to suppress/hold back reason” or more naturally “forcing myself to hold it in.” The key word nulleo comes from Korean 눌러 , which means “press” or “suppress.”

Breakdown

  • 이성 (iseong) = reason, rationality.
  • 을 (eul) = object marker.
  • 애써 (aesseo) = trying hard, making an effort.
  • 눌러 (nulleo) = press down, suppress.

Natural English

Depending on context, it can be translated as:

  • “trying hard to suppress my reason”
  • “making an effort to hold myself back”
  • “forcing myself to stay rational”

Most likely meaning

In a lyric or poetic line, it often sounds like:

“I’m trying hard to suppress my feelings/thoughts and stay calm.”

Because the phrase appears in song lyrics, the exact English rendering can shift a bit based on the full line around it.

Korean-to-English note

If you want, I can also break the phrase into a word-by-word literal translation and a more natural English version.