Stephen Fishbach was the runner-up on Survivor: Tocantins and a member of the jury on Survivor Cambodia: Second Chance. He has been blogging about Survivor strategy for PEOPLE since 2009. Follow him on Twitter @stephenfishbach.

“I love having control.” —Sierra Dawn Thomas, Survivor: Game Changers

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Sierra Dawn Thomas played a disciplined game for more than 30 days, and ruined it in less than 30 words.

It’s rare on Survivor that you can see the actual moment when someone’s game implodes. But as Sierra scrambles to save herself, she winds up with egg on her face. She wisely shares information about her legacy advantage with Sarah. She foolishly shares too much.

At first, Sierra’s decision to approach Sarah seemed tactically smart. She told Sarah that she was sharing a secret that she had told nobody else. She said she had the Legacy Advantage, and described it as “an immunity idol” that could be played at the final six. Sarah was intrigued.

Then Sierra hesitates. She pauses. And in a moment she has probably played back in slow-motion to herself for the last nine months, she says, “I get to will it someone, and you’re going to get a pretty present if I’m gone.”

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Trying to convince Sarah to save her, she gives Sarah a reason to vote her out.

Until those 17 words, Sierra had been playing such a strong game. When she was in charge of the majority alliance, she worked hard to keep her group together. She never pulled any risky moves like targeting her own allies, or made the outsiders feel alienated.

When her alliance lost the numbers, she worked hard to find a new foothold. Her decision to approach swing vote Sarah and share information about her secret advantage was a smart last-ditch effort. It almost worked.

But Survivor is a game of mistakes. You’re tired, you’re hungry and you blurt out the wrong thing at the wrong moment. Who hasn’t done that? For most people, that mistake doesn’t cost them a million dollars, or air to ten million viewers on CBS prime time.

Sarah, at least initially, tells herself that she’s not tempted by Sierra’s disclosure. “When Sierra told me about this advantage, it actually makes me want to keep her now, because she’s giving me information,” she says.

The lady doth protest too much, methinks. Sarah wants to do “the right thing,” because she’s a good person (as we saw when she swam out to help Cirie). But she also knows that in a game for a million dollars, betraying your close friends can be “the right thing.” When Brad wins immunity and Sierra becomes the next target, Sarah agrees with the vote – and meanwhile, tries to ensure that she remains first in line for Sierra’s fortune.

“I love you. You’re my ‘it girl’ out here. On a real level.” Sarah literally says I love you as a way to deceive Sierra. That may be next level Survivor duplicity.

Moreover, when it looks like her it girl/ love interest may actually be saved by Michaela and Tai, (they want to flip on Andrea) Sarah swings the vote around to make sure that Sierra goes home.

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To do so, Sarah uses Sierra’s legacy advantage against her. “She told me she found a legacy advantage, and essentially what it is, is an immunity idol,” she tells Michaela. It’s a moment of perfect dramatic parallelism. Sarah tells Michaela exactly what Sierra had told her. But then, Sarah leaves out the part that Sierra should have omitted – that the advantage functions as an heirloom, and she’s the only person in the will.

Everything goes according to Sarah’s plan, and Sierra is voted out. My favorite moment of the episode was Sarah’s fake look of shock at Tribal Council. She wants Sierra, walking out, to believe that she is still loyal.

It works. “She was honest with me and real with me out here,” says Sierra, never having a clue who truly betrayed her.

I’m not a big fan of the Legacy Advantage. I have always felt it’s too situational. How dull was it last season when Ken shambled up to hand Probst the note, though nobody was remotely targeting him? This, however, was the dream situation for the advantage. One ally betrays another, while feigning kissy-face to stay in the will? Production must have been high-fiving each other.

If this was a good episode for the Legacy Advantage, it was a fantastic episode for Sarah. Until this moment, I had thought she was playing a good game – but I wasn’t sure if she was playing a great one. Betraying her ally in order to get a secret advantage is a signature move for Sarah. It proves she is well-liked enough for people to share their information, and devious enough to use it against them.

Of course the challenge for Sarah – if she gets to the end – will be what happens after everybody swaps stories at Ponderosa. We saw Dawn Meehan in Caramoan use her deep personal bonds to betray people. She then faced their wrath at the Final Tribal and got zero votes.

The Final Tribal, however, is still weeks away. For today, Sarah wins the Fishy Award.