Kids take all the fun out of being sick. I'm the kind of person who rarely ever got even so much as a cold, and when I did, it was a great opportunity to stay home from work, cozy up, and be lazy and miserable... and at least have a little pleasure while doing it. Imagine... sitting in bed all day guzzling hot mugs of TheraFlu and having loved ones cater to your every whim. Bonus points if there was a Columbo marathon on A&E! I might be a sniffling snuffing mess, but that would stop me from having the Best Day Ever.
Move that clock forward to after you have two small children running around the much-too-small house. Think you have time to be miserable? Think again! Forget about hanging out in bed all day, because you've got responsibilities to take care of. Chances are your dear spouse is sick, too, since you've both been infected by some bug brought home from preschool or Kindergarten (oh, the irony). Nobody's got the time to help take care of you.
And, don't forget, the kids have been up all night for a few days with the colds that started things off. Extra bonus points if multiple children had the cold in succession, thus multiplying the misery!
Now get out there and change that diaper... I don't care how sick you are.