They tend to think a "revolution" looks like thousands of people storming the streets, or something like that, when it could just be legislation to give millions of people health care or raise the wage for millions of people to a living wage. The thing is that you're supposed to base your strategy on objective conditions, and what the actual marginalized people are doing, not ideological purity or what you WISH you want the revolution to look like. Even if you're really really far left personally, you objectively look at the sociopolitical situation and align with people who aren't as far to your left but have the people power to get shit done. You're supposed to look at all the axes of oppression, and all the factors that prevent working class unity.
That's why you have "leftists" thinking you can replicate 1917 Petrograd (Whatever you think of communism/Leninism, Tsarist Russia was on a level of shitholery that only North Korea today could match)
I mean, if Angela fucking Davis and Noam fucking Chomsky can do it, I'm sure some pasty Berniebro can too.
Unfortunately, a lot of the "BernieBro" types aren't really socialists in a constructive sense, or have a real passion for social change. H.A Goodman is the classic example, he was a Ron and Rand Paul fanboy before he jumped onto Bernie. They just want to burn shit down because they feel that they deserve something more than what they're getting. That's why the idea of "privilege" offends them so much, because it directly counters their internal narrative.