My observation has been that people tend to rely on their religious beliefs or a rational acceptance of mortality. I'm an agnostic and can't help on the religious front, but I will make a suggestion on the rational front that I've used to explain to others how I'm dealing with my diagnosis and prognosis.

We are all mortal, and we are all dying in the sense that as we age, we get closer to our end. This was true for me and other cancer patients before our diagnosis and continues to be true today. If, for example, we cancer patients were cured of our disease today, tomorrow we would again face other ends that anyone may encounter: traumatic accidents, sudden cardiac arrest, other diseases, etc. There is no way around our mortality.

So, the main difference between facing a poor prognosis now rather than later is that we likely have a shorter amount of time to enjoy what we can, make amends, and such. I hedge with "likely" because there is no way to reliably predict the future. Some different therapy may work better for us, or some new and reliably effective therapy may appear tomorrow that would postpone our inevitable end.

In the words of novelist, Jack London, "The proper function of man is to live, not to exist. I shall not waste my days in trying to prolong them. I shall use my time.”