I never really accepted the notion of dopplegangers until a few years ago. I was sitting down at the top of a mountain in North Wales just taking a break and noticed a guy walking towards me who kept looking at me. He kept staring at me and I found it quite odd, I didn't know him at all but he said "hi" and mentioned a persons name (which I can't remember) I said "hi" back to him but he kept calling me this same name. I didn't respond and then he asked me my name... I told him but he was absolutely convinced I was someone he knew extremely well. He went to the top of the summit and on his way down again he still kept looking and shaking his head in disbelief that I wasn't the person he thought I was.
A decade later I was on a train travelling down through the west coast of Scotland and a woman came onboard and sat two seats away from me but facing me. Geez, she was the absolute double of my wife's mum, her face, hairstyle, style of clothes, physical size and even her mannerisms when she was eating were identical. She was a carbon copy of my wife's mother who had died years earlier.
Since then I have had two more doppleganger experiences. One was my father in law and one was a guy just sitting at Heathrow Airport. The father in law one was an absolute double but had died 15 years back and the airport lounge guy was a double for a friend who I had played table tennis with every week for 20 years.
These people were totally identical in every way to the ones I knew so well. Just to clarify, I have 20/20 vision.