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The day I saw this motorbike and side car I saw three other models. I really like the idea of travelling in a side car, or on the bike. Is that a co-incidence? Some people believe they don't exist and that simultaneously occurring incidents have a logical explanation. Other people believe that co-incidences serve as a reminder or warning. On the whole I usually find a logical reason for co-incidences and hear my inner voice saying 'there's no such thing as a co-incidence'. I have had those experiences however that can't be explained easily. Dreaming of a person or event before it happens. Making friends and relationships with people I have strange things in common with. My husband and I have the same birthday; I'm friends with someone who took the same extraordinary number of driving tests; family birthdays, names and significant dates are very connected.
Using co-incidences in fiction requires skill. They can't easily be brought in to explain part of a plot. That can come across as a weak device. On the other hand starting a piece of work with a co-incidence and then exploring it throughout a story could be intriguing. Jot down a few co-incidental things from your own experience of life. Is there a story in any of them? As a group could they be combined in a plot? Are any of them hard to explain and therefore perfect for a mysterious story?