This is an option that can be toggled before creating a sandbox.
This option would enable parts to have a small chance to show a failure, fuel tanks could leak, engines explode or not have control, and command chips could also do random movements over wings, fins or gimbal.
Obviously there are much more parts that could also have problems, but those are my initial ideas.
Black swan events should be added, incredibly small chance, incredibly dangerous. Eg: full hydraulic failure, in this case, differencial thrust will be needed.