سے طرف کی the time Voldemort went to Godric's Hollow in order to kill the Potter family, his soul was very unstable. He had تقسیم, الگ کریں his soul several times to create his Horcruxes (the Ring, the Locket, the Diary, the Cup, the Diadem were in existence at this point). The act of killing is evil; the attempted murder of a child is worse. When Voldemort cast the Avada Kedavra curse to kill Harry Potter, it deflected off the magical protection Lily Potter had unknowingly invoked when she sacrificed herself to try to protect her son, and was sent flying back to Voldemort. Voldemort did not die when the curse hit him as his horcruxes prevented his death. However, his soul was so unstable that the curse تقسیم, الگ کریں it. The piece of soul - which was unable to survive on it's own - attached itself to the most stable thing in the building; Harry Potter.
Because, when voldemort is in Godricks hollow and casts a spell is backfires and a part of Voldemorts soul is attatched to Harry, the closest living thing around.
Voldemort, in his quest for immortality, wanted seven pieces of his soul, as seven is the most magically powerful number. Soon after learning all he could, he made his diary into the first Horcrux. He then searched out objects from the four founders (the cup, diadem, and locket). Probably around the same time, he used his family ring. As of October 1981, Voldemort's soul was extrordinarily unstable, having been ripped apart so much. As such, when Lily Potter gave her life for Harry and Voldemort turned his wand on the boy, "a piece of Voldemort's soul latched itself onto the only living thing it could find." And that just happened to be a fifteen-month-old baby boy with a scar on his head. Most likely, it was never Harry himself that wa the Horcrux, but the scar on his forehead. Either way, the scar created a link between Harry and Voldemort. (More details can be found in کتابیں 5-7)