Buddhu Hrithik....

  kyon chalti hai pawan
  because of evoporation
 
  kyon jhoome hai gagan
  because of earth's revolution
 
  kyon machalta hai mann
  because of excessive respiration

 
  na tum janno na hum
  but i just gave all the answers
 
  kyon aati hai bahar
  because of change in season
 
  kyon lutata hai kaarar
  becuase of mental tension
 
  kyon hota hai pyaar
  because of fatal attraction

 
  na tum janno na hum
  like i said these are all science phenomena
 
  kyon gum hai har disha
  because u have lost the sense of direction
 
  kyon hota hai nasha
  because of drug addiction 

Poor chap hrithik...being this much ignorant-film line is the only career he can be in.