Despite numerous public opinion polls indicating that California voters would defeat Proposition 8, a proposed constitutional amendment to limit marriage to one man and one woman, Election Day 2008 brought an end to six months of marriage equality for same-sex couples. This paper explores four possible explanations for why Californians passed Proposition 8 despite the polls: (1) poll respondents did not respond honestly to pollsters; (2) some respondents who opposed same-sex marriage were initially reluctant to amend the constitution for this purpose; (3) the campaign over the amendment changed people’s opinions about same-sex marriage; and (4) poll respondents did not initially understand how to accurately connect their position on same-sex marriage with the “right” position on Proposition 8, but that they gained such knowledge over time. This study finds minimal support for the first three explanations and weak support for the final explanation