Few things in life are guaranteed, of that I am certain. I am just as certain that although success may not be guaranteed, failure can be. You may not be gigantically successful in your freelance writing career by writing, writing and more writing, but the absence of writing is a guarantee of failure.
You don't have to take my word for it; Stephen King, a far more successful writer than myself, admonishes the writer to read a lot and write a lot.
If you battle perfectionism as I often do, putting those first few words on paper is almost certainly the bravest act of your day. I am sometimes so afraid of failure that I struggle just to find the "perfect" topic, let alone author an article about it.
Thankfully, more and more often these days rational thinking overtakes the perfectionism tendency and I bravely forge ahead. This A to Z Writing Challenge is an example of this moving forward. I haven't spent hours agonizing over the word I want to use to represent each letter of the alphabet--but not because a part of me hasn't tried to. I've been making concerted efforts to go with my original instincts and move forward.
It depends on how each person measures success, but for me, making an entry each day of the challenge so far spells success to me.