Srila Bhaktisiddhanta Sarasvati Thakura says that a devotee does not care about his own happiness and distress; he is simply interested in seeing that Krsna is happy, and for that purpose he engages in various activities. A pure devotee has no way of sensing happiness except by seeing that Krsna is happy in every respect. If Krsna becomes happy by giving him distress, such
a devotee accepts that unhappiness as the greatest of all happiness. Those who are materialistic, however, who are very proud of material wealth and have no spiritual knowledge, like the prakrta-sahajiyas, regard their own happiness as the aim of life. Some of them aspire to enjoy themselves by sharing the happiness of Krsna. This is the mentality of fruitive workers who want to enjoy sense gratification by making a show of service to Krsna.
Srila Prabhupada's purport to CC Antya 20.52