I've lately been more conscious about the effort required to change deeply held beliefs, in particular the ones you hold about yourself. Being very cerebral I tend to fall back on data and facts in assessing beliefs, and this can be a blessing and a curse.
The next time you confront a belief that you want to change, and you run up against a data point - or maybe a mountain of data, accumulated over decades - supporting your old belief, remember that you generated those data points largely because of the old belief. Understanding that the beliefs led to the actions which led to the outcomes is a very powerful motivator and makes it a lot easier to stay on the path of change.
When they say you can't teach an old dog new tricks, it's partly because the old dog has so many years of having their beliefs reflected back to them from the external world, and accepting that it's just "the way things are".