A history written from surviving letters includes the bias of who could afford to write.

Records survive unevenly, and what survives shapes what later gets called the past. Letters came from people with paper, time, literacy and a reason to expect the letter would be kept. The lives without those things are not absent because they were unimportant, only because nothing was left behind to count them.

When you read an account of anything, ask quietly who was in a position to leave a record. The same question applies to your own workplace and family, where the version that survives may simply be the version somebody had time to write down.