I jokingly use reasons like "I didn't like my initials" to "I'm evading the law" (keeps life simple and explanations short); the actual reason is more tragic...
I lost my wife to an aggressive breast cancer (we would have been married 18 years had she lived another month - we were best friends). As an orphan I had no other living relatives outside of my daughter who graduated from High School at the age of 16 (she is brilliant) and moved on to make a name for herself in this world (today she is a successful programmer, mother and wife).
When I met my new wife, Diane Kratochvil, she was in mourning for the loss of her husband, John Kratochvil (of 15 years - they were best friends). John's family helped me through my mourning period, even though I was in a place he should be. The entire family adopted me and I was honored when they gave me permission to take their name.
I kept Shields in my name so as to prevent total confusion (reference Driver's license below)