Today's wisdom is simple.
It's easy to get riled up in this field, what with publishing supposedly dying (it's not), that folder in your inbox labeled "rejections" steadily growing, and not meeting your daily NaNoWriMo goal. It's okay to rant a little bit about how you wish just once, you'd get a partial request instead of a form rejection. Every writer hits this point at sometime. But, you shouldn't take all the negativity in your life and throw it on others.
I peruse the internet most of the morning, and you wouldn't believe how much negativity I find: writers putting down other writers because they don't have the experience, unpublished writers hating on published writers and saying what they write is trash even though they've never read it themselves, and just an overall distaste toward the industry. You hear horror stories about writers sending hateful emails to agents that reject them, and you read blogs where writers rant for hours about how evil agent so-and-so is and how they should be burned at the stake.
I'll admit, sometimes, it's tempting to rant, but there is a time and a place for it, and the internet isn't where it should happen.
You can -- and will -- end up hurting your reputation as a writer if you act so immaturely on the internet. The internet is like a personal file that can't be thrown away. What you say in forums, on others blogs, or in emails can come back to bite you. It's there forever, and even if you manage to delete every incriminating comment, someone somewhere has already read it, and it may be an agent, your mom, or the secret service. The internet is open to everyone, which means everyone has access to what you say. For a single comment or email, you could be blacklisted by agencies, publishers, or even the writing community at large.
So, be nice. Just as trolling and hateful comments can get you a bad reputation, being helpful and kind can get you a good reputation. Help others when you can and be encouraging to other writers. People don't like listening to other people complain, no matter how good it feels for the complainer to get it out of their system. People do like listening to people who try to help them, who take the time to be courteous and comment positively on their work. Just keep that in mind when you want to rant about your latest rejection or the nerve of that agent for saying your work wasn't fit for their list.