China’s first north-to-south express highway is the G4. It is over 2,200 km long and you can use it to drive from Beijing all the way to Hong Kong or Macau. On a busy day, it looks like this:

Your mind has more than a mere 50 lanes, but on a busy day, the level of traffic is just the same. Each car in each lane represents a different version of you. A version that would make an alternative choice, behave differently, or think another way. But there’s a catch:
Only one lane is called ‘the present’ and only one version of you can drive on it at any given time.