Stanley and Hector are imagining what's on the top of the hill
Then they have to stop because Hector's condition gets weaker and weaker and Stanley can't talk because he hasn't had water in a long time.
the conflict starts when hector collapses
“Higher and higher he climbed. His strength came from somewhere deep inside himself and also seemed to come from the outside as well. After focusing on Big Thumb for so long, it was as if the rock had absorbed his energy and now acted like a kind of giant magnet pulling him toward it” (Sachar 75).
At that point, they are on the top off the mountain and they find water and onions
"It's all my fault," said Zero. "It's nobody's fault," said Stanley. "I didn't know," Zero said. "That's okay," Stanley said. "Just rest."(Sachar 77).