The elimination of chametz has two distinct parts: the search for chametz and the nullification of chametz. Our sages tell us that according to strict Torah law, one of these would be enough. If we search for chametz and eliminate all that is in our domain, then there is no chametz to worry about. And if we nullify our chametz, we have nothing to worry about because the chametz is no longer ours - we have completely repudiated it.
Even so, our sages required both courses. Even if we search thoroughly for chametz, there is a good chance that there will be some nook or cranny which we will overlook, through laziness or simple human fallibility. If we do not also repudiate our chametz, this unfound leaven will cause us to transgress. And even if we nullify the chametz, our sages were worried that perhaps a person does not have complete conviction in his repudiation; furthermore, later on he may encounter chametz and eat it.
The same is true of our bad traits. Fundamentally, we can avoid sin in two ways: we can identify and eliminate our base desires (analagous to searching for and eliminating chametz) , or we can firmly conclude that we will resist our desires and not act on them (analagous to nullifying chametz).In practice, both are needed. Our baser instincts are so pervasive that a person who set out to eliminate all of them would almost certainly neglect some. A person may be successful in identifying a tendency to laziness and then increasing her motivation; she may recognize a tendency to pride and begin to meditate on her own loneliness compared to G-d's greatness. Yet a tendency to anger may remain undiagnosed. This person would remain a slave to her lower nature in this area.
An alternative path is trying to merely defuse our bad traits. A person may adopt various behavioral tricks to keep her anger under control - for instance, counting to ten whenever anger begins to well up. Unfortunately, human nature being what it is this decision may not be sincere, or may not be made with a resolution which makes it lasting.
Therefore, both expedients are necessary. When we come to free ourselves of our bad traits, we must earnestly search them out and strive to eliminate them, and simultaneously resolve not to be a slave to those weaknesses which remain.
Rabbi Asher Meir is the author of the book Meaning in Mitzvot, distributed by Feldheim. The book provides insights into the inner meaning of our daily practices, following the order of the 221 chapters of the Kitzur Shulchan Arukh.