In any change process, beware celebrating change too early. In Kotter's seminal book Leading Change* the change process includes a step to consolidate the improvements to date and highlights the continued effort to produce still more change, even at this late stage.
One of the reasons to be mindful of celebrating success too early is resistance may become apparent that might not have been obvious up to this point. At the first sign of a premature congratulations, resistors will be provided with ammunition to say "I told you so!"
Kotter states: "Whenever you let up before the job is done, critical momentum can be lost and regression may follow." Until the new ways of working are truly embedded into the organisation a change effort is fragile and may regress at speed.
Change in large organisations is difficult in part due to the interdependent nature of how organisation's work. A change to 'A' may require 'B', 'C', and 'D' to change also even if it is only 'A' that will enjoy the benefits. This interconnectedness is a challenge for change agents who need to employ a number of methods to get the right people involved, motivate individuals to adopt the change and to make adjustments as the process progresses.