They were convinced there was so much happening behind the scenes in their favor that nobody was seeing. That they'd go into the House chamber and find a notebook saying "We stole the election. Trump won by a lot! xoxo Nancy" They thought the Capitol police were fellow travelers who would take up arms to hold Pence at gunpoint to overturn the election. They thought Trump would swoop in and direct them like a squad leader in battle. They thought they'd find the Senate in session cowering and pleading for mercy, that they were all thieves and of course Trump was the real president. I mean, it's not like Trump is just going to sit back at the White House with a Coke and watch them get shot.
Basically this:
