I really like this quote from Sharon Salzberg's book, Real Happiness at Work. It recognises the truth of the old Buddhist belief that dissatisfaction is an inevitable aspect of living. But it does so without resentment or even gloom. Instead it asserts that we can live with, and even be happy in, that dissatisfaction.
To do so we need to accept our moments of dissatisfaction as well as those we like. Acceptance here means not fighting with the inevitable reality of the moment. We normally fight reality through self-talk, those imaginary battles we have in our head when we don't like what's happened but can't (or won't!) do anything about it.
Actually, acceptance often leads to change - its seems to direct energy in useful and sometimes powerful ways. Think of someone who accepts they have a drink or drug problem and who ultimately goes into recovery because of this acceptance.
But there's a lot of dissatisfaction in life that we won't be able to do something about. Accepting this enables us to navigate through these dissatisfactions in good shape. That's an important aspect of mindfulness and one that is well worth cultivating.
We can cultivate it by watching out for negative self-talk and by recognising that most of life's dissatisfactions are quickly forgotten even though they may feel terribly important at the time. Mindfulness helps us to step away from that negative self-talk and into awareness of our breathing or what we are physically doing.