Sowmu, my friend and the song Ramaiya Vasta Vaiya of Shree 420.
If we think from the premises of this film this song resembles the pain one is going through during the parting times.
But if we see the song from the beginning the song is being sung by a group of street people who in general does not have anything to loose or not much a thing to gain .Their singing the song indicates their casual interaction with life and easy acceptance of any good or bad. One big teaching which comes from this film is HOPE. Which reflects in a couple of plots of the film e.g. the 100 rupees flat sequence , the hope to get everything back for the poor, getting the love back after all the miss happenings.As we know this film is the journey of a small town guy coming to a big town and lost his naive ness partly due to the circumstances and partly by his inclination to be rich early (which in general every body have) .The first part of the song tries to make him remember the pure soled human with which he came to the city and changed. The second part is used as a comparison between the previous him and the current him.
Now a days these things may look stupid but these words are eternal and have a wonderful meaning always.
These days when love , care kind of feelings loosing its meaning in its true sense these songs are like fresh air and let you float to your childhood days.
Optimism may be off and on for the rich people but are always with the poor. These are kind of songs always remain as a token of good lyrics and unbiased intention to make to meaningful cinema.