The absurdity of the "Bernie wrote the rules" talking point.

[ehrnst]

69. Bernie helped to draft the rules that he's complaining are "unfair."

He worked to neuter Superdelegates by banishing them from the first round of voting, but keeping their participation in a brokered convention. Not surprising, as historical record shows, Superdelegates have not done what told them to do.

The decision to relegate superdelegates — now called “automatic delegates” — to the second ballot in a contested convention consumed the DNC for nearly two years after the 2016 election. Superdelegates overwhelmingly sided with Hillary Clinton, infuriating Sanders’ supporters.

The rule change was widely viewed as a major victory for the Democratic Party’s left flank. At the time, Perez called the delegate overhaul “historic,” while progressive Democrats and many moderates lauded its appeal to young voters skeptical of centralized party power.

https://www.politico.com/news/2020/01/31/dnc-superdelegates-110083

It appears he assumed there would be little to no competition this time around, so a brokered convention wasn't a scenario that he anticipated.

He assumed incorrectly, and now he's upset that the very rules he worked to change to give him more of an advantage against Superdelegates won't give him an advantage at all, and in fact give Superdelegates (who, as history shows, have in the past not complied with his directives) in the current scenario a specific directive to determine, in a brokered convention, who the best candidate will be.

On May 29, 2016, Sanders said superdelegates had the “very grave responsibility to make sure that Trump [is not] elected president of the United States. Vote for the strongest candidate.”

https://www.washingtonpost.com/politics/2020/02/20/bernie-sanders-pushed-contested-convention-2016-now-he-wants-avoid-one/

Where do you propose "blame" for Bernie's frustration lies, if not with Bernie?

Face the facts already.