Both are right in their own way.
We can achieve anything (and this is the most optimistic Hindu thought)
The Vedas clearly say that we have, in our hands, the power of Bhagavan or the Almighty. So, in that way we can achieve virtually anything and everything.
Ayam me hasto Bhagavan; ayam me vishvabeshajo, ayam ShivAbhi
In my hand is the all-round power of Bhagavan (Shiva), power of
healing and power of auspiciousness.
Atharva Veda 4.13.6
The Vedas also motivate us not to look back but to move forward.
MA gatAnam A didhithA.
May i not ponder about the past events.
Atharva Veda 8.1.8
Now since fate or destiny is related to our past karmas, this mantra clearly is asking us to ignore them and move forward.
This is exactly what Swami Vivekananda must have meant.
But the argument that fate is too powerful is not without merits either.
The power of fate or destiny is also too strong:
- I do not know how to perform Tapasyâ; what is the use, then, of my attempting to do so? I am of very bad luck, and thus my good resolve
will not be crowned with success.
- I consider Fate to be the strongest of all; Fie on one’s own prowess! For actions done with effort and hard labour are frustrated
entirely by Fate.
- Time can never be overstepped; See! Brahmâ, Visnu, Rudra, Indra, and others are all under the influence of the Great Time. (Utatthaya's
The Story of Satyavrata, Devi Bhagavatam, Book 3, Chapter 11.
- O King! If what is laid by God in the womb of futurity (a state of things preordained by God in which it is sure to take place in the
fullness of time), be taken as the first-hand proof, then all the
other proofs are rendered null and void. Therefore Fate and human
exertion both are to be undoubtedly taken into account to ensure
success. (Vyasa's words)
Amba Yajna rules Chapter 12, Devi Bhagavatam.
- Though the success depends on Fate, still one should make an earnest effort. If one does not make any effort, fate also remains
asleep. I will therefore soon make out a plan to save my son. 15
(On the battle between Yuddhajita and Vira sena Chapter, Same Purana)
- O kings! No one can cause the death of another. All this world, moving and unmoving, is under the control of Fate. 36-38. No soul is
independent; every one is under the effects of one’s own Karma. The
Pundits that have realised the Truth, say that Karma is of three
kinds, Accumulated, Present, and Prârabdha? This whole world is due to
Kâla (Time), Karma (action) and Svabhâva (Nature); unless the proper
time comes, even the Devas cannot kill men. The men are killed on
account of some cause, immediate; but the Great Time is the real
8-9. O king! Everybody, even Brahmâ, Visnu and Mahes'a all under the
influence of this Karma! And they experience pleasure, pain, old age,
disease and death, joy and sorrow, lust, anger, greed and other bodily
qualities, out of the effects of this Karma, which we call ordinarily
Fate. (Suta's words)
(Supremacy of the effects of Karma, chapter 2, same Purana)
19-20. Effort, application and manifestation of energy are certainly
the duties of man; but their effects are all under the Great Destiny
or Fate. (Vasudeva's words)
13-16. If all the actions are under the control of Fate, then no
effect can come out of any effort; so all efforts are reduced to no
effect. If what is ordained by Heaven is to come to pass then what is
the use of taking recourse to any action and Agnistoma sacrifices,
etc., that are declared to lead to Heavens. Judge! If Heaven or Fate
you consider all-in-all, then the whole Vedas, the revelations from
God’s mouth turn out false; if the Vedas be false, then there is no
reason why the whole Dharma will not be destroyed. ( Devaki's words)
On the killings of the sons of Devaki chapter of the same Purana.
27-51. Brihaspati spoke :-- O Lord of the Devas! O Venerable One! Be
peaceful; have patience; when a difficulty comes, one should not, all
on a sudden, lose one's patience. O Chief of the Immortals! Victory or
defeat is completely under the control of destiny: therefore
intelligent ones should always be patient.
The power of Destiny is exceedingly great and terrible; its influence
cannot be overcome even by the best of the Devas (Vyasa's words)
So, while fate is seemingly almost impossible to defeat we should also always keep exerting. This is what i have understood as the essence of this rather complicated discussion.