Why "this" Keyword does not work inside Javascript objects methods

Almost frustrated about a strange thing, i have created an object with javascript, added some properties and methods to it, and some of these methods are accessing that object properties, i was excepting it work, but for 2 weeks of trying and giving up ,then trying and giving up ( i thought im doing somthing wrong so this is why i kept trying and trying) till i fed up. so i googled about it, and i found this great article Javascript Tutorial - Why The this Keyword Breaks
Its really interesting reading about some of JavaScript internals