The two countries stand to gain a lot, aside from the economic benefit of closer cooperation. They share security concerns, most notably over China and over North Korea. The hard sell here really is the South Korean public. According to one poll, 64% think that an apology from Japan and an investigation into these historic wrongdoings is a prerequisite for that to happen. So managing the domestic politics and the sentiment of South Koreans will be the crucial task for Mr. Yoon if he wants us to stick.