How important is marriage (결혼 結婚), which literally means "to join (結) in marriage (婚)"?

 ANSWER: I think it is at least a "3-thought" (삼사 三思) decision.

The Chinese character 三 (삼) means "three," and 思 (사) means "think" or "thought," so 삼사 (三思) can literally translate as "three (三) thoughts (思)" or "three times (三) think (思)," which means "to think carefully [about something]."

So, since the decision to get married is so important, one should give it more than just "a thought" (일사 一思) or even "a second thought" (이사 二思).

From Dong-A's Prime Korean-English Dictionary