When the helicopter failed to spot him, Prosperi was worried but still sanguine that he would be found. After a few more days alone in the desert, he finally came across a building. He was optimistic that he would find people there, but it was a Muslim shrine that was abandoned. He stayed there for a while and ate bats he found near the roof of the building. He eventually heard a plane and quickly ran out to try to flag it down, but yet again, he went unnoticed and was forced to watch the plane fly away. His hopes were beginning to fade but he continued his journey across the desert.
Many days after becoming lost in the desert, Prosperi came across an oasis. He slowly drank water to help his dehydration. The next day he was found by women who offered him goat’s milk and food. They called the police who quickly came to see who the strange man was. The police were dumbfounded to discover that he was the marathon runner that got lost in the sandstorm because he ended up over 180 miles away in the country of Algeria. He lost nearly 40 pounds over the nine days that he was lost in the desert. While he survived, it took him nearly two years to fully recover. Despite the hardships that he faced during the Marathon des Sables, he entered the race again in 1998 and then in 2012.
What is the meaning of sanguine as it is used in the passage?