I work in a large office block, with maybe 500 other people. Think of all the people linked to that group of 500 people. My daughter works in a large furniture store, her boyfriend works in a large supermarket. They meet/see thousands every day. The chances are, between the three of us, we MUST have met someone who has the virus, or someone who has contact with someone else who has it. It strikes me that you're more likely to have come into contact with the virus, than not.