As a freelance writer, you're only as good as your most recent output. When that output fades from memory, people -- editors and product line developers, for example -- start to forget who you are, particularly when it comes to offering new writing jobs.
I've been lucky so far in that I've had day jobs to support me while further exploring a writing career. The advice "don't quit your day job!" is particularly relevant in a freelancing situation. Job offers come at a feast or famine rate usually, and while a freelancer may be tempted to take any and all such offers that come along, taking on too many at once during the feast times will likely cause the entire body of your work to suffer. It's important to pace yourself.
Even having a freelance gig on my plate at the moment, I'm already looking around for new opportunities. I can afford to be picky right now, but not having work for too long is risky. I'm continuing to send short stories out to open calls, and I have a card game under consideration with one game publisher. Projects like these often take time to move into the final stages, so patience is a good quality to develop.
It's also important to keep writing while waiting. Those projects could fall through for me, so if I haven't continued to generate potentially sellable output, I could be back to square one in my writing career fairly quickly.
Being a freelancer is more complicated than having a 9 to 5-type job, but the rewards sometimes outweigh that dependability. It used to be that somebody could work at a company for 30 or 40 years and retire with a pension; those days are gone, and the lifestyle of a freelancer will likely become the norm rather than the exception for the majority of people.
No matter what else happens when you're a freelancer, don't quit your day job and make sure to read your contract!