This is the 17365th most frequent Korean word.
선에
"선에" means "on the line" or "at the line" in English.
The usage of '선에' in this sentence refers again to a physical line, suggesting a boundary.
선에 부딪히지 않게 조심하세요.
Be careful not to hit against the line.
Here, '선에' refers to a physical line on which placement is advised against due to instructions or rules.
그 선에는 물건을 놓지 마십시오.
Do not place items on that line.
In this sentence, '선에' metaphorically represents a level or standard of performance or expectation.