Impurity is much easier to achieve than Holiness

In Parshat Tzav we learn that if meat comes into contact with something tamei (ritually impure) then that sacrificial meat becomes impure and is rendered unfit and must be burned (7:19). Similarly, pure sacrificial meat that comes into contact with a vessel renders that vessel holy, and the vessel can no longer be used for mundane purposes (6:20). Rabbi Shenur Zalman of Liadi (The Baal HaTanya) notes that in both cases, the impure and the holy has an impact on other items. However he refers us to Rashi on 6:20 that explains that concerning the holy meat, there must actually be a transfer of flavor by means of heat in order for the vessel to be rendered holy.

From here we see the difference between holy and impure. When it comes to the impure, mere contact has a negative effect on others. However when it comes to holiness, it does not rub off and positively affect others so easily. Transfer of holiness requires more effort, it requires heat and drive. Bad habits and traits rub off much more easily and are transferable by osmosis. The same is not true of good habits and traits. Those we have to work harder to gain.