Promises are something that people say they do but not always follow through. Politicians for a long time promise a lot and never follow through and over the years a lot of jokes were made about that. Having said that a lot of promises are kept when people usually believe in what they do as far as I am concerned. People who are true believers in whatever they do are often the people who follow through and for the most part live true to themselves.
People are not perfect, they learn through mistakes and improve and keeping promises are something that takes time to learn it is a skill after all.