There are lots of different jobs in nursing. Some nurses don't even go near sick people. That's a good point. If you get sick of a job, you can brush up on different skills and completely change jobs.
The stuff I remember clearly from nursing school is the, "Nobody said it would be like THIS!" stuff. Nurising is stinky. The stenches are something nobody can prepare you for. The bad news is sometimes (a lot, for me) you have to take a shower when you get home or you end up smelling like a variety of very gross stuff. The good news is you get used to it for the most part (and there is always Vicks.

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I also quickly came to the realization that it isn't a Pollyanna kind of job. The rewards very often don't come from the patients. The ones you can do the most for are too sick to thank you for it - sometimes they don't even know what you've done. And they often don't live to thank you for it. You have to actually derive satisfation from having done it. The good news is that the rewards are great.
Sometimes it is very hard when people die. Especially if you've been with them for an extended period of time. If you happen to really like that patient, of course it is difficult. But I've had patients that I wasn't all that attached to die and end up in tears when they go. After a while, you get used to all the dying, and the death process, but there are always occasions when it hits you hard. They tell you in school not to cry - it is unprofessional. WhatEVER. If you feel like crying, cry. If you don't feel upset, you don't. Don't be ashamed of crying and don't feel guilt if you don't. There is no right or wrong way to react.
The #1 thing I would wish that every nurse had was sympathy for the patients. Always try to treat your patients like you'd want your mom or dad or child treated if they were in that position. Too many nurses just don't care about the person. If you don't truly feel badly for these folks and want, in you heart of hearts, to make their ordeal a little less painful...not only will you not be good at your job, you won't be happy.
Finally, you can't be sensitive. Patients make comments about your personal appearance - if they think you are pretty, ugly, fat, skinny, large (or small) breasted, etc...you are going to hear about it. If the old guys find you attractive and think they'd like to have sex with you, you're going to hear about it. They call you, other nurses, the doctors, the support people - names. No matter what race you are, some patient isn't going to like you based on your skin color, and they'll tell you so. A lot of the times, they just aren't thinking clearly, but sometimes they are.
It isn't like customer service, where you can sit around saying, "I will not put up with this!" If you can't deal with it, you're going to have to find another job...human nature isn't going to change for you. And these people who make mean comments still need your help. You have to rise above it, and take the high road. When you have, you can pat yourself on the back. When you cave in to your baser instincts, find another job.
There is also, like has been mentioned, the fact that people are sick and dying all the time. Morning, noon, and night, 7 days a week, 365 days a year. They don't stop for Christmas and neither do we. If you aren't working PRN, you'll be working holidays.
So, ther are a lot of down sides. I can't speak for everyone about why it is such a great job. But I can speak for myself.
I know that I have done good, helpful, and nice things for my patients. I know that many people's lives and deaths were made a little less difficult by my actions and works. I wholely (that a word?) believe that I have done the work God sent me here to do. I put my heart and soul - literally my blood, sweat, and tears into something I believe to be the most worthwhile work around. Somebody has to do it, and I'm privleged enough to be the one.
I get a lot of compliments - from patients, families, doctors, etc. But the best part is how I feel about myself. My work has purpose and I do it well and with kindness. I can be proud of myself when I lay my tired head down at the end of the day. There is no better feeling.