You do everything you can for your actors, directors, designers, choreographers, etc. every day and, most of the time, they don't appreciate/acknowledge any of your hard work. It's kind of like being a parent: most of the stuff you do, no one even knows about so they can't really appreciate it. But, somehow, we love our job and keep putting ourselves in the same position with varying results. Some casts/directors/etc. are very respectful and appreciate, but 8 or 9 times out of 10 this is simply not the case. However, most SMs are fairly content with not being recognized and put up on a pedestal every time they do something important or praiseworthy. If an SM wasn't a self-motivated, goal-oriented person to begin with, they probably would have chosen a different job.
It takes a special kind of person with a unique temperament be a successful SM. You can't take things too personally (you'd go crazy). You have to remain calm in stressful situations. You have to be the most dependable/reliable/trustworthy person in the company. But at the same time, you have to be personable, friendly and someone the cast/director/etc. can talk to.
As far as "bad" SM qualities...I suppose it's not a terribly good idea to freak out at every available opportunity, especially in front of your cast. It's also probably not a good plan to be a dictator/"yeller" as many people won't respect your authority if you're always lording it over them. I think everyone has their own way of dealing with "divas" but probably one of the worst ways to deal with a diva is to not deal with her/him at all. This will just lead to him/her walking all over you and making you their personal slave/doormat.
So, anyhow, I don't know how helpful (or not) this will be to you. Hopefully more so than less!
-Britney