They believed their own hype and so did their uniparty media that just parroted it back to them.
They considered Wisconsin, Michigan, and Pennsylvania in the bag for them. Her campaign invested little time or money in those states. They did not even do much internal polling. They concentrated on the the swing states. They never knew that Wisconsin, Michigan and Pennsylvania were swing states.
Florida was a swing state and her campaign invested much in that state. When Florida was called for Trump, I knew she was doomed even before Wisconsin, Michigan and Pennsylvania were called for Trump.