Sin is taken lightly by Muslims because they believe that man was born good.  Committing a few mistakes were not really a big deal because Allah will forgive them by the good works they have done in their life.This idea of heaven and hell is very narrow because they believe that every person has two angels recording their good and bad deeds. Going to heaven or hell is the ultimate decision of Allah after they die, by weighing their good deeds and bad deeds. If the good deeds outweigh the bad deeds then the person will go to heaven; but if the bad deeds outweigh the good, that person will go to hell.