? (episode) - Lostpedia: Eko then tells Locke that they will go to the question mark, stating that Ana-Lucia told them in his dream to find it. Locke responds with a look of skepticism, to which Eko asks him, 'Have you ever followed a dream?' Later, as the two are arguing about symbols on the map that Locke had copied from memory, Eko steps on a Virgin Mary statue, and the two stumble before the burned plane with the heroin smugglers. Eko asks what made the plane fall and Locke answers that it was 'Boone who made it fall'. He then ads in a nonchalant derisive ~ self-mocking tone that it was 'a sacrifice that the island demanded'.
I skipped to the last few episodes of season 2
so I was wondering how he had become the skeptic to Eko's man-of-faith. , no longer a believer in meaningful dreams and sacrifices that "the island demanded." I figured it was bcs Ben told him the button does not really need to be pushed... and it appears that's right:

John Locke - Lostpedia:
("Lockdown") ... Locke was thrown into a state of self-doubt when Ben claimed that he never pushed the button and that nothing happened, though his faith in the Island's abilities was bolstered a bit with a conversation with Rose, who made it clear that she was also aware of the Island's healing properties.
In "?", Eko had a dream in which Ana-Lucia and his brother Yemi told him to help Locke and to go to the "question mark". Eko asked Locke to help him find Henry, who had escaped. Later in the jungle, he told Locke that they are really in search of the "question mark." Locke refused to tell Eko what the question mark is, so Eko knocked him out with a headbutt. When Locke awoke, he showed Eko his sketch of the blast door map, and Eko decided that they must find the question mark as shown on the map. Then, they arrived at the Beechcraft in which Boone died. Locke mocked his past ideas and implied that he still blames himself for Boone's death.