1. What if we only had a 50% chance to survive past 30?
2. What if pigeons could speak?
3. What if we had wheels instead of legs?
4. What if reincarnation is real?
5. What if ducks ruled the world?
6. What if we live in a simulation and we will observe it getting gradually shut off?
7. What if boxes didn't exist?
@RayInNJ mentioned round objects on his list, and it reminded me of a Flemish TV show a friend told me about, which I haven't watched: one of the episodes is set in an alternate reality in which boxes don't exist, and some guy invents the concept.
8. What if status seeking was not a thing?
9. What if smartphones became illegal?
Or if they didn't exist at all? It's harder for me to imagine, since they started appearing when I was a teenager. Although I did wait a few years before I got one. Was I better off before that? I don't know.
10. What if I hadn't travelled to Montreal & NYC when I was 16?
My parents somehow let me go there (and paid for it) to meet an internet friend in Montreal and do whatever in New York. It changed my life, and the thought of what my life could have been like if not for that is terrifying.