To kind of swing things back on topic, there have been three major things in my lifetime that have stopped me from riding for varying lengths of time.
Not knowing that bicycling is a valid form of transportation. For much of my life I was carfree but walked everywhere or used public transit. It took an epiphany, like a light in the road, to show me that cycling would be a good way to get places. It's faster than walking and sometimes faster (and usually cheaper) than taking a bus. Nowadays, with so many bike commuters around my location, I think I would have figured this out much more quickly.
Fear of crime. I was victim of an attempted bikejacking on my way home from work. For several months, I gave up on riding after dark. Since I then worked until 11:30 PM, that meant no bike commuting. I took a lot of cabs and bummed a lot of rides before I came to my senses and resumed my riding.
Bad health.This has been a short term problem off and on over the years, usually due to arthritis flares or a right hand badly injured in a bike fall. Now it's more of a long-term issue. I haven't been riding for months now because of a health condition. It looks like it will be next year before I start riding again, if I can meet my goals.