He sounds an almost Buddhist when he argues that dropping desire is the key to interior freedom and ultimately happiness (a problematic term). While all is transitory and passing and suffering is part of life, our attitudes towards these can have a great impact on our well-being.
Difficult to practice but at time circumstances require that we do just that. I won't comment more on it except his famous distinction between what is up to us and what isn't is a very challenging and difficult exercise. Combined with surrendering to fate (different than fatalism) and the overall philosophy contains some valuable kernels of wisdom. Although not perfect, it is a precursor to the dominance of psychology in the contemporary era.
Psychology and philosophy are more related than the positivist empirical tradition of contemporary psychology might wish to admit.