Instructions can be hard
DIY home projects can be pretty difficult. Even if you have an instruction booklet you can follow, experience is the best teacher. You’ll have to make a ton of mistakes before you can get the job right in one try. This is important because if you fail, a second attempt can be quite costly.
Just look at this person’s door. The project involved cutting a hole at the bottom for a kitty door. However, they didn’t realize that they’d flipped the door the other way before measuring and cutting. Now, the only way this person’s cat can get through the door is if it grows wings.