Complex systems are systems whose behaviour is intrinsically difficult to model due to the dependencies, relationships, or interactions between their parts or between a given system and its environment.
fault tolerance isn’t composable
Peter Alvaro
Fun >>>>>>>> Business Critical >>>>>> Safety Critical
Reliability
Doing what is specified
Repeatedly
TDD, Type System, Proof, etc
Safety
Avoiding Loss Events
Financial, Assets, Human life
Systemic property
Not a technical problem only !
Humans create safety continuously through normal work
The Rasmussen Model
Drift into Failure
We build Dynamic Systems
Law of Stretched Systems
every system is stretched to operate at its capacity; as soon as there is some improvement, for example in the form of new technology, it will be exploited to achieve a new intensity and tempo of activity.
Larry Hirschhorn
The above-the-line/below-the-line framework
Mental Model
A few more models if we have time
ETTO
Efficiency-Thoroughness Trade-Off
if you wait until you have found the perfect solution, the system changed too much
better go with a partial one for now
Work-As-Imagined vs Work-As-Done
Incident is your system telling you where these two mental model diverge
Incidents as untyped pointers
Why do things go right ?
Incidents as unexpected investments/probes/experiments
you paid the price already, at least get some sense-making out of it
