there are also security issues to consider. a common example is a bank account. you have a balance, and you use deposit to put in money, and withdrawal to remove money. if balance was public, it could be modified without depositing or withdrawing money. that could be VERY bad.
within a method, you can put checks on things, such as making sure you don't take more money out of an account than actually exists. you can't really do that if you're accessing the values directly. it's about control.
