How does block propagation delay not cause accidental forks? Block propagation delay, it looks like, is about 122 seconds in some cases. If another block is formed before the first block is completed, wouldn't this accidentally create a fork? How would this fork be resolved? Someone's transactions are bound to get lost.
Example:
Let's start with a block A. Say block B was just completed, and is now being propagated.
If, during that delay, someone made a transaction and a new block C was created before block B reached them, wouldn't their blockchain become forked, with A-&gt;C and A-&gt;B? How does bitcoin prevent accidental forks like this?
How does bitcoin prevent accidental forks like this?

It doesn't. Bitcoin make little effort to prevent forks at a technical level, instead relying on the fact that when a fork does happen, it can be resolved by waiting for additional blocks and picking the chain with the most work.
As Pieter mentioned, the mining mechanism itself prevents long term forks. The act of mining extends one chain beyond the other, reducing the shorter chain to a temporary and now discarded fork.
For miners specifically, they put in a lot of effort to avoid this - mining on even a minor fork is inherently risky, as they could lose their blocks if the other side of the fork wins, thus losing the block rewards.
To reduce this risk, all serious miners join high speed links as Bitcoin Fibre. These are specially designed to minimize propagation delay.
No serious mining operation will be looking at propagation delays of 122 seconds - those would only be happening at nodes run by people with absolutely abysmal peering and internet access. For the vast majority of nodes, blocks are received in a few seconds, and for miners, usually in &lt;1s.