I have not heard of a three day method, but I work with toddlers so I see a lot of kids going through the toilet learning process. We give parents a "potty packet" including a check list for signs of readiness. Some of the signs include the child being able to notice when they need to go, being able to tell you, being able to use words like "pee" and "poo," disliking a wet diaper, being able to pull pants up and down, staying dry for at least two hours, and more.
In addition, in the child's brain, myelinization must be complete before potty training can occur. Parents can try and try, but until this happens, it won't work. This means that long motor neurons reach from the Betz cells of the motor cortex in the brain down to the urethral sphincters, which control the flow of urine. For the child to be able to control this themselves, these long motor neurons must be fully covered with a white, fatty sheath, called myelin. This myelinization allows voluntary control over these muscles and may not happen until about 24 months of age.
Anyway, children are developmentally ready to potty train at different ages. If they are ready, some children will take a few weeks. If the child is not ready, it can take much longer. I'm not sure what kinds of readiness signs your son is showing or what the circumstances are, but you may need to just give it a break for a while and come back in a month or two. I would avoid power struggles, as it can make it a stressful and tense situation for him. If your son is actually ready, it really could just take 3 days. If he's not, it may be a waste of time.
Many parents use rewards, but I personally do not agree with this because this is a normal body function that everyone does and I don't think rewards really have anything to do with using the bathroom. I've seen so many kids learn to use the potty as "just something you do" rather than something you get a reward for.
Remember, learning to potty train really is a LEARNING PROCESS and, like most other things, not something that can be taught overnight. Even children who are mostly potty trained will have accidents from time to time and this is normal. Just keep in mind, no normally functioning child will grow up to walk down the isle wearing diapers! Just keep it positive and it will happen in time. Sorry this doesn't have anything to do with the 3 day method, but I hope this perspective helps.