Not giving is the lowest Kelipa:
The Yitush/Gnat is the lowest Kelipa that exists and is the most distanced from Kedusha than anything else. This is expressed in the fact that the Yitush does not defecate what it eats, and hence shows that it only intakes and does not give. This is the greatest form of selfishness and impurity, as the side of Kedusha is all about giving others.
 Tanya Chapter 24