What is a single point of failure on a farm?
Short answer: A single point of failure is one part of the farm whose failure stops an entire service, because nothing else can take its place. One well. One pump. One road in. One person who knows how the irrigation timer works. Finding them before they fail is one of the highest value things a small farm can do.
How to find them
Take one service, such as water to the livestock. Trace it from source to use: well, pump, power supply, pressure tank, main line, valves, troughs. At each step ask: if this fails, does the service stop? Is there another way? If the answer is "it stops, and there is no other way", you have found one.
Do not forget the non physical ones: a single key, a single password, a single person.
What to do about one
You have four choices. 1. Remove it. Add a second source or path. 2. Reduce the chance. Better maintenance, inspection or protection. 3. Reduce the impact. Spares on the shelf, stored water, a written workaround. 4. Accept it, on purpose. Write down that you know, and why you are living with it for now.
The fourth is a real option. The mistake is accepting it without knowing.