Bhagavad Gita Verse 33, Chapter 3

sadrisham cheshtate svasyaaha prakritejnyaanavaanapi |
prakritim yaanti bhootaani nigraha kim karishyati || 33 ||
 
Even a wise person will behave according to his own nature. All beings follow their own nature. What can restraint do?
 
sadrisham : according to
cheshtate : behave
svasyaaha : one's own
prakriteh : of nature
jnyaanavaan : wise person
api: even
prakritim : nature
yaanti : follow
bhootaani : all beings
nigraha : restraint
kim : what
karishyati : will do
 
Shri Krishna here addresses a critical point, which is that even the most well-read and educated person will find it difficult to practice karmayoga. Why is this so? It is because inbuilt tendencies and urges inside us compel us to act against our will. These tendencies comprise our lower nature. Note that the lower nature is also called "prakriti" here, which is different than the prakriti that we saw earlier.
 
All beings - plants, animals and humans - are born with an innate set of traits. In humans, these traits are manifested in the body, mind and intellect. These traits are a product of our vaasanaas, which are impressions created by past actions.
 
It does not matter whether one is wise or foolish, rich or poor etc. All human beings are born with vaasanaas. These vaasanaas are "thought generators". They cause thoughts about the material world to arise in our mind. And once a thought arises, it results into desire and action as we saw in the second chapter.
 
Therefore, Shri Krishna says that mere restraint of actions will not result in eradication of desires, since the vaasanaas will continue to generate more and more thoughts. And direct suppression of thoughts is next to impossible. Many people try to repress thoughts and desires in the hope of progressing spiritually, but like a spring that is pushed down, that strategy backfires very easily.
 
But then, should we give up our efforts altogether? That is not the case. For example, you cannot teach tiger to be non-violent and eat grass. But you can change his behaviour to a certain extent through repeated training. Similarly, the vaasanaas can be channeled in the service of society. Like judo uses the opponent's strength to subdue the opponent, karmayoga uses the energy of vaasanaas to extinguish themselves.
 
So therefore, Shri Krishna gives us a way out. Even though all of us have tendencies that can drag us lower, we can analyze those tendencies and overcome them through the technique of karmayoga. Having explained this, Shri Krishna gives us the exact location of our enemies, these lower tendencies, in the next shloka.