Kim Kardashian is reflecting on her personal life and career as she celebrates a major career milestone. The reality star and SKIMS mogul, 41, appeared on the cover of the Sports Illustrated Swimsuit issue this month, which marks her first time ever appearing in the magazine. In a video promoting the new issue, Kardashian opened up about the things that bring her joy, including parenting her four children with her ex-husband Kanye West. "I'd say that the most rewarding part is that, unless you're a parent, you really don't get how challenging it is," she explained. "There are nights where you just are like, 'I don't want to do this, I don’t want to adult anymore, this is really hard.' Every kid is crying, and no one will go to bed."