If we doubt a thing happened or not and we are not certain about it then the default ruling is that we ignore the doubt as if nothing happened right? Does this rule apply to all matters? Ustadh this is according to your saying 'certainty does not affect doubt.'

The rule is that certainty is not removed by doubt, so you go back to what you were certain of before the doubt. If you were sure you had wudu and doubt whether you broke it, you still have wudu, and if you were sure you had none and doubt whether you made it, you have none. The scholars apply it in purification, prayer, divorce and other matters, except that doubt after finishing an act of worship, and constant doubt, are ignored.