[Dilemma] Protecting myself from being taken advantage of at work resulted in my coworkers just getting the brunt of the additional workload and bullshit. Is there a way to protect the self without screwing over other workers?

Inspired by this sub Ive tried being more assertive at work and refusing work that i was killing myself over just because. Ive succeeded and now im no longer working weekends. Great right? Not really because I learned the work just got shifted to some other poor bloke. Does it have to be this way? Does pushing back for whats fair only end up with jsut shifting the misery to someone else? Doesnt that make me part of the probleM?