The greatest demotivator I encountered in school was my second (of 3) PhD advisor. I was in a chemistry group, and we were studying photocatalysis: how to make materials that used solar energy to split water into hydrogen and oxygen. The experiments for this research involved 6-8 hour long sessions of getting up every half-hour, turning a knob, pressing a button, and saving a file on a computer for the measurement of hydrogen produced. This was maddening to be chained to the machine for so long. I proposed an automation system, and was told that if I could do so for under $5k, I could do it. I got a quote for all the necessary parts for ~3k.
Leading up to this, my advisor had also stated that I needed to put more into my group presentations. I worked really hard to polish this particular one, which coincided with the other issue.
All of this culminated in a rather catastrophic group meeting wherein he called my presentation sloppy, and said that we weren’t going to automate things because he had just been to visit the leaders in the field, and none of them automated things. I have never felt so downtrodden and undervalued as I did that day.
He could have told me what he wanted in the presentation specifically, rather than simply calling it “sloppy,” and he certainly could have shelled out $3k to make his research more reproducible and improve his grad students’ lives. Otherwise, he could have at least had a better reason, like “we can’t afford this” - the excuse of “the leaders aren’t doing it, why should we?” was pretty lame.