Bhagavad Gita Verse 22, Chapter 18

yattu kritsnavadekasminkaarye saktamahaitukam |
atattvaarthavadalpam cha tattaamasamudaahritam || 22 ||
 
But, that by which one clings to a single object as if it were everything, without logic, unconcerned with truth and trivial, that is called taamasic.
 
yat : by which
tu : but
kritsnavat : as if it is everything
ekasmin : single
kaarye : object
saktam : clings
ahaitukam : without logic
atattvaarthavat : unconcerned with the truth
alpam : trivial
cha : and
tat : that
taamasam : taamasic
udaahritam : is called
 
A teenager will not eat food unless her parents agree to let her go to a late night party. A businessman is so keen on protecting his profits that he will stoop to physically harming his competitors. A politician is so keen on lining his pockets that he will sell state secrets to the enemy. A hospital will order unnecessary and even potentially harmful tests on its patients in order to increase its bottom line. We read such stories everyday in the newspapers. Unfortunately, they are all too common these days.
 
There is a common theme in all these stories. A person is holding onto something trivial and giving it so much importance that they will stop at nothing to get it. The logic used to justify such actions is perverted. Such people have an extremely narrow vision, and are not at all concerned with any the bigger picture. Shri Krishna says that a worldview, a knowledge that displays such characteristics is considered taamasic. He hesitates to even use the word knowledge here, using a pronoun instead.
 
Let us compare the types of knowledge we have seen so far. A saattvic knowledge reports that there is one eternal essence, one aatmaa, one self in all. Raajasic knowledge reports that there is a different self in each body. Taamasic knowledge reports that the body itself is the aatmaa. Furthermore, anything is justified for ensuring the integrity of the body, including causing physical harm to others. Such people will never accept any other viewpoint, and hold on to their perverted viewpoint ceaselessly.