If you haven't met someone who does something "for no reason" then you haven't met enough people yet. In a strictly cause-effect sense, of course he has a reas

If you haven't met someone who does something "for no reason" then you haven't met enough people yet. In a strictly cause-effect sense, of course he has a reason for not wanting a bank account. That is a sentiment and some finite set of causes resulted in him feeling that way. But "for no/whatever reason" is not a philosophical statement, it's just shorthand for "for reasons he/she doesn't want to disclose" or "for reasons he/she isn't even aware of." If a thousand tiny but unknown (to the reader) experiences have given Mr. Grand a deep emotional aversion to financial institutions, "for whatever reason" is about the best you can do as a description.