This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
So you started from your context node and looked for a child element whose name was Hello. Maybe you found that Hello element and maybe you didn't, depending on what your context node was. Then you looked for a parent of that node which was a Bye element. Presumably that Hello element isn't a child of any Bye element; it certainly isn't if that's your whole document.