Just as the organs of a human body have many cells, a mission-critical application has many parts. Let's say that among the good lines of code are bad bacteria, which we'll equate with the Year-2000 bugs. When corporations began searching out and fixing Year-2000 bugs, their programmers had to examine each line of code individually to find the bugs. That was hard work, and very slow. Just as doctors have studied the human body and found useful antibiotics to combat bacteria, software programmers have developed tools that do much of the work of preparing an application for the year 2000.
Some tools scan code line by line and make changes.
Even if a corporation does an excellent job preparing its applications, it is still likely to see some Year-2000 bugs. Corporations that are well-prepared, and those that are not, need to develop contingency plans. If you go camping, you plan for the obvious challenges, such as mosquitos and the hot sun. You also anticipate a variety of possible contingencies, such as sprained ankles. In addition, a wise camper expects to respond and innovate to handle unanticipated situations.