If a person’s life is according to his poorva vasana/destiny, How can a guru help him?
We may have taken thousands of births and committed millions of sins. No matter how colossal that figure maybe, it is unquestionably well within the realm of the finite. Guru’s boundless grace though, is immeasurable, limitless and infinite.
The tapas and grace of the Sadguru can make up for his Karmas and takes him to the path of liberation quicker.