Both Ruki and Sukai hate to lose.
Ruki wants to win at everything, even in janken. If Ruki lose at game, he will practice a lot in silent and doesn’t show it so he can win next time.

He has always thought that showing your hard work isn’t cool and embarrassing so he doesn’t show it and works hard in shadow/silent

Sukai also hates to lose but there is also a time when he gave up quickly. If he thinks, “Ah, I can’t do this” he will let it go right away. It’s not that he’s running away and just do things that he’s good at, but he evaluates his capability and judge from that.

But if he has the members and the group’s future in his mind he will try and work hard for their sake. If you want to earn something, you have to compensate (by practicing, working hard) to gain it