As stated in Srimad-Bhagavatam (10.14.58):

This material world is just like a big ocean. It begins with Brahmaloka and extends to Patalaloka, and there are many planets, or islands, in this ocean. Not knowing about devotional service, the living entity wanders about this ocean, just as a man tries to swim to reach the shore. Our struggle for existence is similar to this. Everyone is trying to get out of the ocean of material existence. One cannot immediately reach the coast, but if one endeavors, he can cross the ocean by Sri Caitanya Mahaprabhu's mercy. One may be very eager to cross this ocean, but he cannot attain success by acting like a madman. He must swim over the ocean very patiently and intelligently under the instructions of Sri Caitanya Mahaprabhu or His representative. Then, one day, he will reach the shore and return home, back to Godhead.