One of the clearest indications that a person reads little and doesn’t hear much formal English is a failure to use the right preposition in a common expression. You aren’t ignorant to a fact; you’re ignorant of it. Things don’t happen on accident, but by accident (though they do happen “on purpose”). There are no simple rules governing preposition usage: you just have to immerse yourself in good English in order to write it naturally.
See also different than/different from/to.
List of errors