In Fallout: New Vegas, there's a Vault 11 where the first overseer told everyone they needed to sacrifice somebody or else the computer would kill the whole vault. The dwellers did not take kindly to that announcement, so guess who became the first sacrifice? That's right, the overseer. But why didn't he admit it was a lie in order to save himself?
Judging by the recorded speech of an election officiate (here on the Fallout wiki), the overseer definitely knew about the sacrifice and likely knew he would be the first sacrifice, but either did not know the reason behind it or just didn't disclose it:
We want it to make sense. To understand why the vault's mainframe will kill us if we do not offer one of our own as a yearly sacrifice. To fully comprehend why we continue to have these elections....
Well I've been through the archives, and I can tell you you won't find the answer there. You'll find an account of the first overseer, who entered the vault as the only citizen aware of the sacrifices that would have to take place. But he didn't have the answers either. If he did, surely he would've foreseen the citizens' anger when he broke the news. Surely he would've guessed that they would want to choose a sacrifice democratically, in the way that we citizens are accustomed to washing our hands of terrible deeds, and that his name would be at the top of the polls, and that the simultaneous vacancy of overseer and martyr would forever fuse the two positions here in Vault 11. But he didn't. He had the answers no more than any of us, and the records state that after the citizens discovered that the sacrificial chamber's password was his wife Betty's first name, and its door was unsealed so he could be offered as the first sacrifice, he walked down into that room crying like a child.
I can only wonder if there are no answers to be found, and we are just going along with this because we don't see another choice.
Assuming the archives are right, the first overseer knew going into the vault that they would be asked to make sacrifices, however he was clearly very distraught on the way to his death. Either he was like the other citizens and didn't know he had a choice, or he was upset that the citizens would make the same choice every year.