The Compendium of Caraka 1.15.5

1.15.5

tamuvāca bhagavānātreyaḥ śakyaṃ tathā pratividhātumasmābhirasmadvidharivā 'apyagniveśa yathā prativihite sidhyedevauṣadhamekāntena tacca prayogasauṣṭhavamupadeṣṭuṃ yathāvat nahi kaścidasti ya etadevamupadiṣṭamupadhārayitumutsaheta upadhārya vā tathā pratipattuṃ prayoktuṃ vā; sūkṣmāṇi hi doṣabheṣajadeśakālabalaśarīrāhārasātmyasattvaprakṛtivayasāmavasthānatarāṇi yānyanucintyamānāni vimalavipulabuddherapi buddhimākulīkuryuḥ kiṃ punaralpabuddheḥ tasmādubhayametadyathāvadupadekṣyāmaḥ samyakprayogaṃ cauṣadhānāṃ vyāpannānāṃ ca vyāpatsādhanāni siddhiṣūttarakālam //

To him the venerable Ātreya said: "It is possible for us or for those like us, Agniveśa, to arrange things in such a way that, once arranged, the medicine must inevitably succeed, and to instruct properly in that excellence of application; yet there is no one who would be able to comprehend it when instructed in this way, or having comprehended it, to practice it or apply it accordingly. For subtle are the transitional states of the doṣas, medicines, habitat, season, strength, body, diet, suitability, mind, constitution, and age, which, when reflected upon, would confound the intellect even of one with a clear and broad intellect, let alone one of small intellect. Therefore we shall properly instruct in both: the correct application of medicines, and later, in the [section on] successes, the remedies for complications when they have gone wrong.