Bhagavad Gita Verse 31, Chapter 18

yayaa dharmamadharmam cha kaaryam chaakaaryameva cha |
ayathaavatprajaanaati buddhihi saa paartha raajasee || 31 ||
 
That by which one improperly understands the difference between dharma and adharma, what should be done and what should not be done, O Paartha, that intellect is raajasic.
 
yayaa : by which
dharmam : dharma
adharmam : adharma
cha : and
kaaryam : what should be done
cha : and
akaaryam : what should not be done
eva : also
cha : and
ayathaavat : improperly
prajaanaati : one understands
buddhihi : intellect
saa : that
paartha : O Paartha
raajasee : raajasic
 
A soldier goes through weeks of bootcamp training. A chef takes decades to hone her craft. Surgeons are in their thirties before they perform their first official operation. A musician can take a lifetime, and still have room to grow. In all these cases, we see that it takes years to fully understand what and how to perform actions in one's career. Unless such knowledge is gained through a competent teacher, and years of one's life are put in, the quality of our work output will never reach perfection.
 
Shri Krishna says that the science of action, the karma yoga, needs to be studied with similar dedication and guidance. Unless we learn what is our dharma, what is our duty towards this world, we will be swimming in an ocean of ignorance. Are our actions ethical? Are they carried out for selfish ends or are they performed selflessly? Are they entangling us further in worldly affairs, or are they taking us closer to liberation? We need to understand karma yoga, the science of action, to clearly understand all this.
 
Therefore, one who has not received this knowledge will always be unclear about what is dharma and what is not. Consequently, they will always be confused whether to act or not. Confusion will creep in if we forget our dharma and get swayed by egoism and attachment. Arjuna's attachment to his family members, the Kauravas, triggered this confusion with regards to his duty as a warrior. Shri Krishna had to teach him the science of karma yoga to remove this confusion. So then, whenever our intellect gets confused about whether to act or not, we can assume that it is raajasic, tinged with selfishness.