3holelover
Forgive me, please, if this is too much of a rabbit trail, ....but I always thought the whole idea of the Swiss Cheese analogy was to call attention to the number of slices that could have stood alone to prevent an accident, but didn't.
No single slice alone can be blamed.
The anaology is a simple communication tool for those that don't work everyday in safety analysis and/or risk assessment.
It also begins to work with simple minded lawyers who like to paint things in winners and losers
In actuality a more descriptive analogy would be a flow diagram where some things are in series with conditional gates while others are in parallel.
When most of us use the simple swiss cheese analogy it's taken as a conditional shield in series. That is if it works the failure condition is arrested (minimized, mitigated etc.) to a point wher a more serious condition is avoided.
More importantly the investigation seeks to indentify as many contributing factors as possible and somewhere along the line safety proffesionals (not necessarily investigators) need to pareto what layers of cheese can be improved for the largest improvement in safety versus available resources (tools equipment, skilled labor, out-of-service time etc.).