There’s a pattern to it. I don’t know what it is, and I’m not sure anyone knows consciously. But for example, when creating new words (eg. fantasy/sci-fi context) there usually isn’t any confusion as to what that word’s gender will be, it just sounds bad with the wrong pronoun. There are a few exceptions of course, same as “autobus” and “avion” which technically have a gender assigned but people toss a coin every time.