Some authors aren't great at writing characters. They tend to be composed of a subset of the author's own attributes. There's nothing wrong in that itself; I generally don't go for character-driven plots or novels and find bildungsromans rather tedious. But I dislike it when an author decides to put in a character who is super smart or creative or whatever, but then the character is basically not super smart because the author themselves isn't. All the other characters might go "ooh" and "aah" at whatever clever thing the character said, but looking at it from an outside perspective, it very often isn't all that brilliant and it makes the reactions rather cheap and unbelievable, detracting from not just the genius-character-who-isn't, but many of the other characters as well.
I hated, hated, Arthur C. Clarke's novellisation of 2001: A Space Odyssey and its sequels for this reason. "Oh look, this character now has near-infinite wisdom and intellect and has evolved so far beyond humanity that he is less similar to us than we are to bacteria! He is almost literally a god, having unimaginable power over time and space! So now he's going to act in a very predictable, petty, average, limited adult kind of way, and constantly forget to use his powers to solve whatever silly non-problems he faces, despite one of his powers apparently being the ability not to forget his powers. Maybe writing in that last one was a bit of a mistake?"