In her book "I Know Why the Caged Bird Sings," Maya Angelou wrote, "Hoping for the best, prepared for the worst, and unsurprised by anything in between." A similar but shorter quote with a religious spin can be heard multiple times in "Prisoners," first spoken by Keller, then later repeated by Loki, "Pray for the best, prepare for the worst." The religious angle ties into Holly Jones's war against God and the overall commentary on religion being made by the film.
The quote also speaks to the mindset of the prepper community, which Keller counts himself a part of. From his basement full of survivalist supplies to the key emergency whistle that he gives his daughter, Keller is someone who considers himself prepared for the worst. The only problem is, Keller wasn't truly prepared for the worst. He was unprepared for his daughter to be abducted, and when the unimaginable happened, he spiraled out of control and did things he probably would have thought himself incapable of beforehand.
The "Pray for the best, prepare for the worst," quote also ties directly into the ambiguous ending of "Prisoners." The last time this quote is voiced aloud is by Loki in the film's final scene when speaking to the technicians who are working on digging up the backyard of the Jones home. The ambiguous cut-to-black ending without revealing Keller's fate allows the film to have it both ways and offer up hope without ruling out the worst outcome.
