Fluff time: is it easier to pick up a habit or break one?

Time to time I know people who for one reason or another try to get into the habit of doing something. For instance, they get a new puppy so they have to get in the habit of doing things to keep maintenance of the pet or keep it from escaping. Sometimes it is a new job and they have to remember to do certain things before they leave work because they will be working the usual time they did them. Or they try to break a habit, like leaving their tools laid where they lay, and not put them away, wipe them down, keep them from the weather etc. It could be the habit of not taking leaving food junk in their car from the commute home. To you, do you believe in general (not necessarily how you handle it); do you believe habits are harder to form, or to break?