yayaa tu dharmakaamaarthaandhrityaa dhaarayaterjuna |
prasangena phalaakaankshee dhritihi saa paartha raajasee || 34 ||

But, that fortitude by which one holds on to duty, sensual pleasure and wealth, O Arjuna, desiring reward as their occasion arises, that fortitude is raajasic, O Paartha.
yayaa : by which
tu : but
dharmakaamaarthaan : duty, sensual pleasure and wealth
dhrityaa : fortitude
dhaarayate : one holds on
arjuna : O Arjuna
prasangena : as the occasion arises
phalaakaankshee : desiring reward
dhritihi : fortitude
saa : that
paartha : O Paartha
raajasee : raajasic
Pursuit of duty, sensual pleasure, wealth and liberation, dharma, artha, kaama and moksha, are considered the four goals, the four purushaarthas, of a human life. Over time, the importance and even awareness of liberation as a goal was lost. Most of us pursue the first three goals only. Shri Krishna says that the fortitude or the will power that enables us to pursue these three goals is termed as raajasic dhriti, raajasic fortitude. It is termed raajasic because it is oriented around the attainment of the goal, and also, the personal reward that comes to us when that goal is accomplished.
On college campuses, we always know of a few people that spend the entire day in the canteen, and do not attend even a single class. But somehow, many of them study for a few days prior to their exams, just enough so that they pass their tests. Some of them get very good at playing the guitar so that they can impress others. Yet others are spending their time buying and selling shares online. In all these cases, they seem to have a will power that only works when there is an occasion for pwesonal reward that is in line with their world view, their raajasic jnyaanam. The will power, the fortitude does not work all the time, especially for anything selfless or altruistic.
Another way to look at fortitude is to assess the type of thoughts that our intellect holds on to, and the type of thoughts it rejects. In the prior example, all three types of students know that a lecture is going on daily. Such a thought will arise in their mind every day, like it arises for every other student in the campus. However, the intellect chooses not to act upon that thought, and conequently, no action follows from a discarded thought. Instead, thoughts about sensual pleasure and accumulation of wealth are held on to, and are acted upon. Everything happens at the level of the mind and the intellect, and that is why the mind is given so much importance in the Gita.