My first thought was that dṛṣṭi, viewing reality as it is, would be easy after one clears their mind of emotional thoughts and refrains from consuming mind altering substances. Then, my mind remembered and fantasized about confusing contingencies. "What is dṛṣṭi to the mentally impaired?" For example, can a psychotic, whose mental state is all-are-enemies, know dṛṣṭi? Can a person who hallucinates from lack of sleep know dṛṣṭi? A few times, my dreams have been realistic enough to cause me to be bewildered for a bit after waking...was it a dream or real? Has a dream of mine surreptitiously passed for real? Can anyone always know dṛṣṭi?
Experiences and thoughts shared by several people are likely to be real, but mass hallucinations do occur. Similarly, events that repeat are more likely to be real, but sometimes dreams recur. We must be realistic about knowing reality.
Is there a parable or poem about this idea?
HHDL: "My confidence in venturing into science lies in my basic belief that as in science so in Buddhism, understanding the nature of reality is pursued by means of critical investigation: if scientific analysis were conclusively to demonstrate certain claims in Buddhism to be false, then we must accept the findings of science and abandon those claims."