Seems like there are a lot of rules with canning... what if you just wing it and make something up without a recipe? If it doesnt explode or turn green it should be ok?
There's a lot of rules for driving a car too, except for canning you are allowed to kill yourself without requiring a license first.
The purpose of "canning" is to pasteurize the food, which is to kill the spores that cause bacteria, mold, yeast, and fungi's so they don't grow in your nice jars of food while they are sitting there on your pantry shelf at room temperature, especially those nice ones called E.Coli, Salmonella and Botulism.
Yes, most of those nasties will cause some form of spoilage and evidence of their hard work so you will see it before taking a mouthful -- which would be a shame if that happened to all your jars of food because you didn't process them correctly -- but there is one nasty that is odorless, tasteless and colorless and often shows NO evidence of its existence.......Botulism toxin.
The Botulism spore is NOT killed by cooking or even processing in a Boiling Water Canner. It is totally resistent to heat. Fortunately it does not grow in high-acid foods so as long as there is no tiny piece of improperly processed low-acid food, water, or oil that didn't get processed correctly, you are safe.
To kill the Botulism spore requires a temperature above 240 deg.F for a certain period of time, which can only be obtained with a pressure canner, so that is what is done for low-acid foods.
Yah, lots of rules, but easy rules, to make sure you and your family are safe from poisoning yourselves.