It's not 'what you believe,' or 'what you're supposed to believe,': it's 'what no one believes, but we make you say anyway.'
Brainwashing 101. It's not about making you believe, it's about making you so afraid that you keep lying until you believe the lie.
No one on the left actually believes Joe won far and square. If anyone believed the lie they wouldn't be so afraid of investigating the lie.
Facebook, Google, ect spend 4 years spreading quicky disproveable lies about Russian collusion. But right before the 2020 election, talking about foreign collusion or voter fruad was deemed to be hate speech. Funny how afraid they are of us talking about it. If they believed talking about election corruption was evil, they coulda pulled the plug on Russian collusion as soon as it was disproven. It's still up. Guess how many CNN articles on Facebook get censored for referencing disproven Russian or Ukraine conspiracy theories about Trumpy?
In Pennsylvania the constitutionality of the election was in question because the left used an executive order to erase the part of the PA constitution requiring Elections be held in person. For those not familiar with constitutional law: the PA constitution can only be changed by super majorities in the legislature bodies and general elections. In other words: it's impossible for the Governor to change how elections are held a month before the election.
When Trumpy brought it to the PA supreme court, they responded: yes it's illegal for the governor to change voting law, but we still won't hear the case because that would mean throwing out millions of votes simply for being illegal.
The 'we won't hear the case because that would be admitting we cheated' response is the only proof anyone needs that it was rigged. If anyone one the left believed it wasn't rigged, they woulda taken the cases. The simplest way to prove you cheated is the refuse to investigate accusations of cheating.
TLDR:
They don't want you to believe. They don't believe. They want to accept the brainwashing. Communism only works if you parrot back whatever the party says.