The way I read it is that they are using 'luck' and 'risk' in the colloquial sense, where 'risk' equates with 'danger' and 'luck' equates with 'good fortune'.

The way I read it is that they are using 'luck' and 'risk' in the colloquial sense, where 'risk' equates with 'danger' and 'luck' equates with 'good fortune'. Basically they are saying that, in a probabilistic outcome, we are comfortable acknowledging that a venture may encounter somewhat random danger, but are uncomfortable acknowledging that they may encounter somewhat random fortunes.