A big problem with writing for a living is how hilariously little money you make. An example: my wage as a writer over the past three years averages out to maybe $0.50 an hour.
Unless you're both incredibly lucky and talented, you're not going to make much money in this business. And so it's a simple and obvious reality that you'll have to think carefully about how, exactly, you will support yourself as a writer.
And how you respond to this specific problem will say a lot about your determination to write. Will you use it as an excuse or as a delaying tactic, and allow a solvable problem to keep you from achieving your goals?
Or will you choose solutions? Will you ruthlessly reduce your expenses so you don't need as much money? Or ruthlessly reduce your other commitments so you can create time to write in addition to your job that pays the bills?
Best of all: How about using a combination of both of these tactics to get yourself in a financial position where you can reduce your paid work obligations and dedicate still more time to writing?
Don't let money be just another thing stopping you. Solve the problem creatively and constructively, and get back to work.