Question

This author has decided to tell the reader right away what happened to Gregor Samsa. However, there is still a mystery that makes people keep reading. What do people want to know?
Why this happened 
Who Gregor Samsa is 
What Gregor Samsa sells 
Who is in the picture

Answer 1

Why this Happened The Author Does This To Grab the readers into reading it

Answer 2

The mystery that makes people keep reading The Metamorphosis by Frank Kafka is why this happened.

One day, Gregor Samsa wakes up transformed into a huge insect. This is an unusual and very strange phenomenon, especially because, at the beginning, the main character is worried about his job and the authorities rather than being worried about his recent metamorphosis. In that way, the reader needs an answer to this phenomenon since the very first page. Furthermore, the story is narrated in third person limited perspective, which increases the reader's interest in the book since the narrator is able to get in Gregor's head and also show his feelings. In that way, the reader comes to understand the character's circumstances along with him. Therefore, for the reader, the most important thing is to find out why Gregor became an insect rather than figuring out who he is or sells or who is the lady in the picture.