Somewhere, in one of those bicycle magazines in an article on one of those training plans that I never follow, I read it takes so many times or days of doing something to develop a habit. Can't remember how many times, but I just googled "habit" and one guy claims the number is 66. I'm a bit skeptical of claims like this, so I like this answer I also found on the internet: It depends.
I don't know how long it took me, but somewhere along the line it became a habit to get up in the morning and ride to work. Like others, I started bike commuting a few days a week. I'd wake up and think...do I want to ride my bike today? Oh I don't know, I'll have to get my bag ready, maybe bring a change of clothes, check my bike. Maybe not today.
But then I figured out I get to and from work in about the same time it takes to drive to work and park, or take the bus, or get a ride to work from my wife. And it's cheaper - well my wife doesn't charge for driving me to work, but I usually take the bus home after getting a ride to work. And it's funner than riding the bus or driving. It's funny - I might be tired after a long day of work, but once I get moving on the bike I wake up a bit.
So I learned to have my bike and bag always ready to go. I get up in the morning like normal, shower, make a lunch maybe and throw whatever else I need in the bag and get on the bike and ride.
Well, I wrote this before I broke the little bone in my hand, but my bike and bag are still ready to go whenever I am.