“Beliefs, behaviors, assumptions, and attitudes do not change through study, conferences, seminars, and training classes; they change through repeated action. This is not dissimilar to breaking unhealthy habits such as smoking or overeating. The consistently repeated lean actions and restraint from doing old non-lean things are undoubtedly ‘painful’ in the beginning” (source: The Kaizen Event Fieldbook by Hamel pages 61-62)
There are two reasons you need to use small repeated steps to create change. First is that you want to eliminate old bad habits the only way to truly do that is to replace them with a new habit. The second is that the only way to develop a new habit is to constantly repeat something till it becomes like breathing, and that takes time and many repetitions. If you go out and try to instantly make one big change human nature will win out and we return to the old ways almost instantly.