"We become what we think about most of the time, and that's the strangest secret." - Earl Nightingale
Dreaming is not bad. In fact, visualization has the strength to let one achieve one’s aim. It is said that if one gets dreams of a rich man meaning that the dreamer wishes to become rich. Similarly, if a person gets dreams of marriage, probably he is waiting since long to get married.
It is quite interesting that a person always wants to become someone else. He may want to become happy if he is sad, wants to become single if he is in a relationship, and so on. What is lacking in us, we always dream of that and want to achieve that. In this striving and pining life ends, and we are still involved in the rat race.
Hence, it is wise to dream big, dream of even becoming big, but not something just because we lack it.