There's a big difference once you decide and commit to doing something every single day (or every second day, etc.) compared to doing something whenever you feel like doing it.
If you decide to do something whenever you feel like doing it you'll constantly be pondering about whether or not you should actually really be doing it today.
Needless to say that we'll come up with dozens of different reasons (and excuses) as to why today isn't a great day for doing it.
And in the long run you won't be doing it for very long because you're busy answering the wrong questions.
Questions such as...
"Should I do it today?"
"Do I have time for this?"
"Is it really that important?"
"Is it even good enough?"
And of these questions take away momentum instead of building momentum.
Because the answer to all of these questions is almost always "No"...
On the other hand if you commit to doing something every single day (for example) you'd have to answer an entirely different question.
So instead of asking yourself all of the above questions you'd be asking yourself this...
"How am I going to do it?"
And that's a whole different question that doesn't have "No" as an answer...