One thing I noticed about my son is he is not afraid of anything. Just like what he's doing in the following video.
Honestly, while looking at him doing it, I was more afraid than him. While I was taking the video, I am giving my husband a look to make sure that nothing harm will happen to our son. But Abi was fine and even after that video, he kept coming back to that same stair and tried to climb without any hesitation.