The context here is software development. Depending on what field you are in, I would tend to agree with you that it might either not be possible or a bit harder.
That said, even in software, you don't always 'have the authority' to do that other job. But does that matter?
Example: you're the junior, new to the team. When the team does backlog maintenance, everyone just slaps some estimate onto the barely defined ticket and calls it a day. Sprints slip all the time because tickets "explode" once you actually start working on them. The team lead does nothing about it, the PO couldn't care less, he just screams at everyone when none of the tickets are done at the end of the sprint.
The junior could just resign himself and play along. Or he can start asking "dumb questions" during backlog maintenance. I.e. start a proper discussion. Suggest tickets to be split etc. The bad team lead and PO might ignore this and even actively try to get back to just slapping on estimates, not actually do the splitting or say "yeah I'll do the splitting by the time we do sprint planning" and then obviously nothing ever happens.
Do it yourself! Offer helping out, to give them a chance to be part of it. They might refuse or try to "pull rank". Ignore them. Split the tickets. If you can't do it before a sprint starts (e.g. cause they'll notice and try to pull rank), split them after you've started on one of those bad tickets. Split it into 3 nicely sized ones and at the end of the sprint you can show that hey, ticket 1 is finished, ticket 2 is almost done and ticket 3 isn't even started yet. We can release the functionality of ticket 1 to customers even!
You've just done all of the following:
Shown that you're not the junior you've been hired as but much more!
Ignored the team lead's authority when it became clear that even when shown the proper way, he's not going to act
Ignored the PO's authority when it became clear that even when shown the proper way, he's not going to act
Let's take this to the call center:
Folks quit these all the time, like you said. Even the shift leaders or managers. I don't know enough about call center operations to know what the equivalent tasks of the little story above are but I do know from experience w/ some of our guys that it's totally possible there as well. We had a really great QA that came in through the call center. Started as a regular rep, became a shift lead, moved into QA and then became a BA. He was awesome at that. Knew everything by heart or was able to quickly try it out in-product. Heck the department lead came in through the call center as well. Similar trajectory but didn't move over to the software side and stayed on the business side.