does a fighter have a iron chin all his career

some maintain it, others lose it for a variety of reasons. some people have a chip on their shoulders or have some psych issues and can walk through a punch that later in their careers they couldnt take. mike tyson is a perfect example of this. watch some of his older interviews. ive seen some where he discusses being a nut and walking through razor ruddock's shots and not feeling anything and then when just didnt give a **** and his heart wasnt in it he said the shots just hurt and he didnt want to take them anymore.