Pronouns are the words in a language like I, thou, he, she, it, we, ye, they, and so on. Ido was made from Esperanto, and all of Esperanto's pronouns end in -i. The people that made Ido thought that they sounded too much the same and that it might be too difficult to hear sometimes. Also, most languages have two ways of saying "you" so they decided to have two ways of saying you. Lastly, they decided to make a pronoun that can mean "he" or "she". Some languages like the Finnish language and the Estonian language have something like this.