The most challenging part for me was always to sit down and do something every day. For one thing, I don't really have a schedule that lends itself to "every day;" I tend to go more in sits and starts. On a good day, I can easily turn out 10K words of decent enough prose... but then I might draw a blank for several days. When I get in the groove, I tend to GO... but then I grand to a halt and find it hard to get started again.
Good for you for completing all six years you've tried... that's impressive!
Thank you :-). I find NaNoWriMo helpful to hash out my first draft, but afterwards I always struggle with editing and querying. I am hoping to self publish this year's NaNoWriMo novel, will try to find and editor who can help me polish it.