The first reason I talked about why teachers cry was frustration. That's from a need not being met. The teacher needed strong leadership from her administrator instead of being given all the work the administrator didn't know how to do. That was compounded by the inability of that administrator to assist that teacher with any of the questions they had or duties they perform on a daily basis. This also leads to overstimulation which I'll go ahead and conflate with being overwhelmed. Weak administrators create more work for teacher and support staff.
The second was hopelessness. That's teachers being completely overwhelmed by the sheer magnitude of the battle they are called to engage in every single day at the classroom level. The hardest thing about teaching is watching poverty happen in real time and feeling powerless to stop it.
Feeling overwhelmed happens when we over book our life. Some of it is our fault. We take on too many responsibilities, don't know how to be efficient, we care too much about people and events we can't control, we can't prioritize so we try to do everything/refuse to let anything slide for a day or two, and whole host of other reasons. Independently, these things are annoying, but usually manageable. You know that corworker that's always walking way too fast and just seems busy for no reason? They're functional but they're frantic internally. The overlap of these reasons is what causes the deluge of tears I've seen teachers create in public.
The best advice I got from a 30+ year veteran teacher was to not take school negativity home with me and to have a sense of humor. It's a work in progress, but it's kept the salt water mostly inside my body for the last few years.
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DISD Teacher Hopelessness Tears
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Refusing to leave Dallas ISD at school