Rust is the common name for even more common Iron Oxide. Iron loves to combine with oxygen and you just don't find nice billets lying about to make swords with, which is why ancient people who found big meteors said 'thankyou God' and made ceremonial and important tools out of them. I'm still waiting for a Playboy Bunnie to fall in my arms to get that religous. Our best, most lovingly cared for Blades want to go back to being iron oxide- the traitors. They do this with 3 elements; iron, air and water which acts as the electrolyte to facilitate this process. Pure water, or super heated water makes a poor electrolyte, which is why a good wash or dumping surgical tools in an autoclave is beneficial. But combine water with carbon dioxide, or better yet salt ( seawater, blood, sweat) or even acid rains from all our pollutants and Mother Nature is standing there with open arms to welcome her child back. You can slow things down by introducing other metals to SLOW the process. This is our so called stainless steel. Notice it's not called rustless, unless your german and call it rostfrei. I can destroy any wonder steel, given time and indifference. Other older methods are simple variations to keep that electrolyte from doing it's damage, wiping the blade dry, creating a temporary ( oil) or permanent ( paint and even stable rust formulas called bluing as in firearms and other finishes) protective layer. Some knives will even acquire a patina of a thin protective film from chemical interaction with, ie potatos. So thats it. To reduce rust, keep your knife clean and dry. This includes fingerprints from admiring friends, humidity, falling into the Clyde river or storing them away carelessly. I guarantee if conditions are bad enough the best cared for knife will rust. But by then leather and cotton are mildewing and our toes glowing in the dark. So don't feel bad if it happens.
In 500 years some kid will find our Woodlore's battered remains, sell it to the British Museum, use the proceeds for a scholarship and get expelled for packing a Ray Mears the VIII's lazer