In the series Lost, when John Locke is trying to crack open the hatch, his leg gets pierced but he does not feel anything. He later tries to pin his leg and burns his foot and still feels nothing. How did he not realize that his legs have no senses earlier, when walking in the water etc.?
I think when he had the metal in his leg when trying to break the hatch window, there was a theory that the island itself was trying to prevent Locke from doing certain things. I believe that the island taking back Locke's cured back, thus preventing him from climbing up to the crashed beach-craft and ultimately saving his life, killing Boone in the process. Once Boone was injured Locke managed to carry him back to the cave for Jack to help.
The island needed Locke and did what it could to protect him.
I think @thonnor is right but there are some details that I think need to be clearly stated so in attempt to clarify things I'm adding my own answer.
First of all you have to understand that Locke lost the feeling in his legs temporarily. When he was struck in the leg from the shrapnel, this was only the beginning of him losing this feeling. He didn't notice anything before this because he had not lost the feeling in his legs yet.
It gradually gets worse, leading up to him being unable to walk and causing Boone to climb to the plane and fall and become "the sacrifice the island demanded". I agree with the sentiment that the forces of the island caused this temporary loss of feeling in order to prevent Locke from climbing to the plane on his own and being killed because he had another purpose to fulfill.