तथा च दु:खं मूढानां वृथाहङ्करणं परम् ॥ १८ ॥
vidyate viduṣām api
tathā ca duḥkhaṁ mūḍhānāṁ
It is observed within the material world that sometimes even an intelligent person is not happy. Similarly, sometimes even a great fool is happy. The concept of becoming happy through expertly performing material activities is simply a useless exhibition of false egotism.
It may be argued that an intelligent person can expertly perform pious activities within the material world and thus never experience suffering, since unhappiness is caused by sinful or impious activities. However, we often observe great suffering even among pious, intelligent persons, because they sometimes fail in the execution of their duty and sometimes consciously or unconsciously perform a forbidden activity. With this argument the Lord refutes the theory that simply on the strength of material piety one may remain perpetually happy without Kṛṣṇa consciousness.
On the other hand, we observe that even the most foolish or sinful persons sometimes experience happiness, because even those completely dedicated to sin sometimes accidentally perform pious activities by inadvertently traveling through a holy place or helping a saintly person. The material creation of God is so complex and bewildering that even those dedicated to piety sometimes commit sins, and even those dedicated to sinful life sometimes perform pious actions. Therefore, within the material world we do not find absolute happiness or unhappiness. Rather, every conditioned soul is hovering in confusion, without perfect knowledge. Piety and sin are relative material ideas that bestow relative happiness and unhappiness. Absolute happiness is experienced on the spiritual platform in full Kṛṣṇa consciousness, or love of God. Thus material life is always ambiguous and relative, whereas Kṛṣṇa consciousness is the actual platform of perfect happiness.