Will definitely has a part of it; but, I think even greater is a sense of purpose. I strongly believe that the carefree in this world have such to a strong degree while those of us that seem to go from trouble to trouble are lacking.
I look at the healthier more successful and happier times in my life and am struck at the realisation I had a higher sense of purpose at the time. THose times I have struggled with ill health I seem to have lost it.
My former psychiatrist told me once that this was something I strongly needed to work on; sense of purpose and also resiliancey.
My sense of purpose is in fact improving and with it a measure of confidence and happiness. I went back to work a year ago and unfortunately that killed it for me and I fell into the depths of anxiety and despair again. Frankly, I no longer ticked. But it has now been several months since I brought that work to an end and once again things are improving and yes, I feel as though I were ticking again.