In the case of the verb parāji 'to be tired or weary of', that which becomes unbearable, is called apādāna kāraka,
When the verb जि to conquer, with the preposition para has the sense of 'becoming tired or unbearable' it governs the ablative case of the thing become unbearable. As अध्ययनात् पराजयते he finds study unbearable.
Why do we say 'that which becomes unbearable.' Observe शत्रून् पराजयते he defeats the enemies.,