You like and respect your boss. He's fired unfairly and you're asked to take his place. Do you? Well, yeah. It's a dog eat dog world. But I would like to add here that this is all hypothetical, I don't want to become a principal, so I don't see this situation happening to me. Also, I don't thonl you can just BECOME principal. I'm sure its a big drawn out mess. But if I had some other job, yeah I would.
You're a cop. Fellow cops are selling illegal drugs. The Chief's in on it. Do you blow the whistle? What kind of drugs is it? Pot? Crack? I think it depends. Yes, cops need to uphold the law, but your fellow cops are the ones who got your back and keep you from getting shot, I don't want to mess with that unless I have to. And seriously, some illegal drugs are just silly to be illegal. Lets get some priorities.
You and a colleague are competing for a promotion. You discover he made a serious mistake which can be corrected. Do you alert him? Probably not. It depends on our history, if he/she would help me out. I'm not going to just hand my promotion to someone else.