I think it's because the contract marriage started out with mutual protection. Many others are about getting money, or a house, or squashing a scandal or enhancing their career or some other quite selfish reason.

Here it's: I'll protect your life vs I'll protect you way of life. Seemed a good enough (and very likeable) reason from the start.

I like couples who try to look out for each other.

Oh my god, that killer makes me laugh for the wrong reasons! He’s going to end up either dead or in prison, so his son is going to be all alone in this world. What a smart dad.

From what I gathered Jak Doo is hiding mostly because of his sense of guilt rather than because he doesn’t want to be exposed. 15 years ago he refused to live in the mountains and was going to Seoul when his grandpa ran after him to stop him and that’s when the grandpa was hit by a truck of doom. JD didn’t have any money for hospital bills so he sold their signature stamp to Eric’s dad. But then grandpa died and I guess JD was too traumatised and riddled with guilt so he shut himself out from the world.

I think JD doesn’t want to be found because then he would have to acknowledge that he’s indeed Oh Hyuk, a grandson that rebelled against his grandpa. Whereas when he lives as a simple JD he can get by life like that.

I’m not sure what exactly his deal with Eric’s dad was. Maybe he agreed to make those instruments for them when he sold the stamp?