[uyt]

Is it possible that the projections themselves affected the outcome? If people saw that they had a comfortable lead, they wouldn't be as motivated to turnout.

Then the polling results might ironically be more accurate if people believed in them less.

[listenallyall]

Yes they can affect the outcome, but the opposite direction than you described. People who feel their candidate is doomed to lose don't turn out. People like to vote for a winner.

edit: To be clear, when polls overwhelmingly suggest a landslide, it suppresses votes from both sides. But a much higher proportion of the losing side will choose not to vote, thus inflating the gap.