Can being certain really mean true non-doubt?

It is said that scientists used instruments to determine that the Earth is oval-shaped, and almost everyone believed it—and it seems to be the kind of belief that is held with certainty, as if such belief had become deeply rooted and unchangeable. If someone does not believe it, others will even debate with him, and even mock and ridicule him. But this is still not true belief and true non-doubt. Belief has many levels; some people even firmly believe without doubt, convinced beyond any uncertainty, without the slightest hesitation. But without personal verification, all such belief belongs to blind faith and superstitious faith, not verified faith through realization. Therefore doubt still exists, only it is deep and hidden, not easy to observe. 

Knowing that the Earth is oval-shaped is merely hearsay, not something seen with one's own eyes; it is knowledge the mind consciousness has acquired through hearsay. Since the manas has not personally seen it, doubt has not been eradicated. Even what many people see with their own eyes may not necessarily be true and real; cases of seeing wrongly are extremely numerous—what the eyes see is not necessarily real—so the manas's doubt cannot be eradicated. Once some other condition arises and it is said that the Earth is actually not oval-shaped but rhombus-shaped or triangular, quite a few people's former belief will waver and turn into disbelief. Why can faith change? Because there has been no personal realization. No matter to what degree the mind consciousness is convinced, it is unreliable; once conditions change, the mind consciousness's doubt appears. Why? Because the manas never believed in the first place and doubt was not eradicated. Once conditions change, without the support of the manas's personal realization, the mind consciousness becomes fickle and loses its backbone—or rather, the mind consciousness's backbone has always been the manas, and at critical moments it invariably turns with the manas. Only by truly seeing the Earth, by genuinely witnessing the Earth's shape from an overall and macroscopic perspective, can the manas eradicate doubt and give rise to faith. In the future, even if conditions change, the manas will still firmly believe without doubt, and then the mind consciousness will follow the manas in firm, unwavering belief; even if the mind consciousness has doubt, it will not take effect, and it will still trust the manas. 

Some people say that as long as you yourself are convinced that you have eradicated the view of self (satkāya-dṛṣṭi) and have no doubt, you have attained the srotāpanna fruit. How childish and laughable such a claim is! Is the ordinary person's firm conviction without doubt reliable? If it were reliable, why are sentient beings so fickle, changing their belief at the slightest disturbance? If the ordinary person's conviction and non-doubt were reliable, why did the Buddha say, "Take heed not to believe your mind; your mind is not to be believed," and that only upon attaining arhatship can one trust one's own mind?

Those recorded in history who have confirmed for others the eradication of the view of self and the attainment of the fruits are, first, the Buddha himself during the Buddha's lifetime, and second, the Fourth Patriarch Prajñāgupta after the Buddha's parinirvāṇa. The Buddha need hardly be mentioned: with immeasurable wisdom, unlimited supernatural powers, and omniscience—with the ability to know others' minds and the recollection of past lives (pūrvanivāsānusmṛti)—he could know and see the thoughts of all sentient beings exactly as they are. Whether or not his disciples had attained the fruits, the Buddha could know immediately without even meeting them. As for the Fourth Patriarch Prajñāgupta, he had not only attained the fruit of arhatship but also possessed great supernatural powers; he even personally subdued Māra Pāpīyas's various provocations, restoring purity to Buddhism. Given the Fourth Patriarch's realization of liberation and his powers of recollection of past lives and knowing others' minds, he could of course also know immediately whether his disciples had attained the fruits, without error. Others who lack realization, whose wisdom and realization are insufficient, and who have no supernatural powers or spiritual might, are probably unable to observe another person's mental state exactly as it is, and therefore cannot confirm for others whether they have attained the fruits. Those with extremely profound wisdom, who have attained the fruits countless times over lifetime after lifetime, and who are rich in experience, can, even without supernatural powers, truthfully confirm for others the timing and circumstances of attaining the fruits; apart from such people, no one else has the ability or qualification to confirm attainment for others. How much less can ordinary people confirm themselves! Lacking experience, their misjudgments are simply unavoidable, and the consequences are unimaginable. 

Practicing the Buddhadharma demands even more pragmatism and rigor than worldly affairs; one must not treat the Buddhadharma as child's play, thinking it is very simple. Nothing is more difficult than the Buddhadharma, because sentient beings have been engaged in worldly affairs for beginningless kalpas and are utterly unfamiliar with the Buddhadharma; moreover, with layer upon layer of karmic obstructions, the obstacles are often far greater than we can imagine. Therefore, studying Buddhism and cultivating practice in a down-to-earth manner is our duty, so as not to add further karmic obstructions and afflictions and sink even deeper into the abyss of birth and death.