One of my labmates used to be the "star student". Super smart and productive, really engaging to talk to etc. However, it seems like overnight, he's become a totally different person. He's stopped coming into lab for multiple days in a row, has stopped making any progress, and is starting to complain a lot. He seems very frustrated with our advisor and the lack of support, and bad-mouthes him every chance he gets now. I'm pretty sure our advisor has noticed, but is just ignoring this or even avoiding him. I'm afraid this student might be dropping out soon. This isn't really affecting me so much, but I'm just wondering why someone would change so suddenly. As a new grad student, I hear a lot about the stress of grad school, and I'm concerned about whether this is a common occurrence? It wouldn't stand out so much, but he was actually one of those "oh, he's going to open his own lab one day" type person. What can I do to avoid a similar burn-out, and is there anything I can do as a colleague? Out of curiosity, is there anything the PI should do?