I know why a lot of people try to potty train early (from people I have talked to). Its because they are terrified that they won't be reliable potty trained by the time they start nursery at age 3. All of a sudden they go from a nice playgroup when the staff are happy to change nappies and cope with accidents, to an environment where having accidents is frowned upon and seen as a big problem. So they think if they start earlier, they will be ready in time. They don't realise that pushing with it too early can give a child a complex about it and make them more likely to have problems in the future.