Man bites dog
The banks’ reaction was an unfamiliar one by modern standards. They lobbied government to be allowed to issue new equity. They retained earnings, building up secret reserves: Mr Capie and Mr Billings show that actual capital was often twice the level of published capital.
While dog-bites-man is often and familiar, man-bites-dog is not. The latter is as unfamiliar as the banks’ reaction, which was to issue new equity.
strength in numbers
An idiomatic expression to mean an emotional and morale strength drawn from a group of people. Here it means the strength (health) of a bank depends importantly on the numbers (ratios), which are the proportions of capital as against the total assets.