Take it from me, I'm procrastinating here.
The first thing you need to realize is that they can't fire you. THEY CAN'T. You can fail, you can be miserable, you can throw your money off a bridge and into the ocean (metaphorically speaking... or literally, it all kind of bleeds together) but grad school is not like real life. Do not believe anyone who begins a sentence with "In the real world..." whose personal 'real world' is academia. Academia is to reality as frozen yogurt is to ice cream. They have some passing similarities but any idiot can tell the difference fairly quickly.
So, to get myself back on track: firing. Yeah, you can't be fired. So when some smug-ass professor says something like he's the stand in for your future boss, feel free to ignore that. He's not. What he should be is your mentor or something, but if he just said that thing about being your boss he is definitely not a mentor.
The next thing that's helpful to know is that sometimes, while you're attending grad school, you might also begin being a real adult person with a real career. Fuck, if you're lucky you'll have a career prior to grad school and grad school will be some weird masochistic icing on the cake of your life. Should this happen, know that none of your professors will ever really understand that you must prioritize things like "rent" and "bills" and "being the primary breadwinner" with your academic "career." (See what I did there?) Instead, they will literally say things like "It might help if you took a year off work."
(You could even — hypothetically of course — build up a company from literally nothing to earnings in the $80,000/year mark in the three years you're in grad school, and it wouldn't matter. Because your MFA would be more important than that. HAHAHAHAHA.)
My third piece of important life advice on being in grad school is that your professors are humans with lives and goals of their own and of course they're fallible. I mean, it should be obvious, but sometimes it isn't... Because you walk into the hallowed walls of scholastic pursuit and you feel like it really means something. And it does! But it doesn't mean professors are magic. So of course they are tired, overworked, and — yes — selfish as fuck just like everyone else. Which is a really long way to say: don't take things personally. If you think a professor doesn't like you (guess what they probably don't) realize that who the fuck cares and move on as quickly as possible. They're not moral arbiters! They're just people.
My fourth and most important grad school wisdom to impart is this: The decisions you make as a graduate student really have to be your own. Sometimes there are excuses and sometimes there aren't, but to be honest it doesn't matter. You're an adult and life requires flexibility and shifting priorities. To pretend as though it doesn't — like grad school will always be the most important thing in your life while you're doing it — is delusional. If grad school is important to you (and if you're paying for it, it fucking well should be) then good, but that doesn't mean it has to be more important than everything else in your life. Find your grad school balance and don't let anyone make you feel shitty about it.