Here is a documentry about UK's Kirkland Laing, who once beat the great Roberto Duran. Laing had lots of potential, but never had the dedication and disicpline to accomplish his potential.

UK writer Steve Bunce tracks Kirkland down, to see what his life has become.(Note this was made a fair few years ago)
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Seen this a few times.

He was a great fighter. To be honest, It's worse then seeing what Tyson has become. At least Tyson has a decent house and a healthy lifestyle.