Ask any old pilot to explain the theory behind his flying, he will not be able.
I can and so can many of the experienced aviators on this forum plus many hundreds I have flown with over 42 years (of which 35 have been as an instructor).
Knowing how to act appropriately comes from quality training and practice - especially when under stress from complex scenarios or emergencies.
If you are an engineer then I assume you were taught in some detail and weren't expected to just 'act appropriately' when managing or fault finding complex systems - you relied on detailed knowledge.