This advice applies to everyone in every job. Unless you are delivered terrible news or punched in the soft parts, you should not cry at work. Or at least not anywhere where anyone can see you or hear you. 

But there is a larger significance to the concept of not crying on the job in entertainment, and that has to do with being strong and being professional. Not just literally crying, but crying as in not bringing your A-game. Getting a writing job means you have entered the big leagues. And in the big leagues, you are expected to perform at a high level, to be your most badass self. That's what you've been hired to be. You are expected to solve what problems you can on your own before bringing highers up into it ( * does not apply to sexual harassment or bullying which should be reported ASAP. ) You are expected to do whatever homework you need to do to be able to keep up in the room without being asked to do it. You are expected to contribute ideas to the writer's room with the frequency of all the more experienced writers (but with deference to them... this is a complex concept... more to follow.) You are expected to take notes maturely -- or, how about this? -- gratefully and implement those notes as though they were your own brilliant ideas about which you are thrilled.

Sometimes high expectations can make a person want to curl into the fetal position and whisper 'I'm a fraud and I can't do this. Someone please pay my credit card debt please please." Remind yourself that you can and will rise to the occasion because you have worked hard for this job, and that hard work and the hard work you will continue to do at the job mean you DESERVE IT. And then if you want to cry tears over your good fortune, your gratitude, go ahead, but please do it in your office with the door closed. That's right: your office.