Why double bonds set the oxidation rate
A fatty acid oxidizes at the carbons next to its carbon-carbon double bonds, where hydrogen atoms are easiest to abstract. Saturated fats have no double bonds and are the most resistant. Monounsaturated fats have one and are intermediate. Polyunsaturated fats carry two or more, and the methylene carbon sitting between two double bonds is especially vulnerable, so oxidation rate climbs sharply with the number of double bonds.
This is why a fat's degree of unsaturation, not just its category name, predicts how readily it forms lipid peroxides and off-flavor breakdown products.
Heat, time, light, and oxygen as multipliers
Oxidation is a chain reaction, so the same fat degrades faster with higher temperature, longer exposure, more dissolved oxygen, and light. High-heat repeated frying is a worst case for polyunsaturated oils because it stacks several of these factors at once.
Antioxidants such as tocopherols and storage in cool, dark, sealed containers slow the process but do not eliminate it. The takeaway from the diagram is comparative stability, not a claim that any single fat is harmful or safe in isolation; dietary fat choices involve more than oxidation alone. General educational information, not dietary advice.