"An  extremely  strange,  but  common,  feature  of  many  software  projects  is  that  for long  periods  of  time  during  the  development  process  the  application  is  not  in  a working  state.  In  fact,  most  software  developed  by  large  teams  spends  a  significant proportion  of  its  development  time  in  an  unusable  state.  The  reason  for  this  is easy  to  understand:  Nobody  is  interested  in  trying  to  run  the  whole  application until  it  is  finished." Ref.pend.