We were discussing riding the bus to a place that depending on traffic is a 20 minute car ride from SF, or a 2 hour car ride in the worst case scenario traffic.

There are a few bridges that connect SF to other places across large bodies of water, the Bay Bridge and the Golden Gate Bridge. These bridges do not provide a dedicated lane for the buses. These bridges act as a choke point for traffic. As a result, the buses are not reliably on time, because the traffic is hard to predict and it depends on whether or not people have a car accident that evening.

As I mentioned in another comment, these buses do not have bathrooms inside. So you are spending an unpredictable amount of time standing at an unsheltered bus stop, often with no bench to rest on, followed by an unknown amount of time on the bus.

The buses come infrequently enough that if you go find a restroom after waiting a while at the stop, and the bus comes while you are gone, it will be a decent chunk of your life spent waiting for the next bus to come as well.

This might be fine if you're on vacation and you just wanted to explore the Bay Area, but if you live here and work here, this is just too much time!

If you have a car, there is essentially no upside to taking the bus in this situation, which means if you are greedy and choose to drive instead you contribute to traffic by taking up more space on the road.

In contrast, if you choose to take the train, you know exactly how long the trip is going to be, because there's no variable traffic disrupting the schedules. It's predictable. It's convenient. Sometimes the train might get stopped for one reason or another, but the trains come so frequently that this is rarely an issue.

Before your trip, you're also inside a train station, which is sheltered, has seating, and even often has bathrooms.

There's a sign telling you clearly how long until the next train arrives, you don't have to count on something on your phone to find out.