Srimad Bhagavatham : 5.5.7.
Even though one may be very learned and wise, he is mad if he does not understand that the endeavor for sense gratification is a useless waste of time. Being forgetful of his own interest, he tries to be happy in the material world, centering his interests around his home, which is based on sexual intercourse and which brings him all kinds of material miseries. In this way one is no better than a foolish animal.
In the lowest stage of devotional life, one is not an unalloyed devotee. To be an unalloyed devotee, one must be freed from all material desires and untouched by fruitive activity and speculative knowledge. On the lower platform, one may sometimes be interested in philosophical speculation with a tinge of devotion. However, at that stage one is still interested in sense gratification and is contaminated by the modes of material nature. The influence of maya is so strong that even a person advanced in knowledge actually forgets that he is Lord’s eternal servant. Therefore he remains satisfied in his householder life, which is centered around sexual intercourse. Conceding to a life of sex, he agrees to suffer all kinds of material miseries. Due to ignorance, one is thus bound by the chain of material laws.