A psycholgist-friend of ours used to say, "Pain is inevitable; suffering is optional."
I think she meant that we as human beings have to undergo a certain amount of pain in this 'vale of tears' we call life on earth, but that we don't necessarily have to undergo the mental anguish of suffering, which has to do with worry and the fear that the pain I have today will only get worse, that my life is coming to a sorry end and is probably not worth living (since I can't imagine life without pain.)
As I think of the many people I know who undergo chronic pain greater than mine along with discomfort of the worst sort, such as crippling arthritis with no hope of remedy, I wonder if they have a choice about whether or not to suffer. Isn't some suffering inevitable? Isn't that why the great religions preach compassion (suffering with)?
For Christians, the passion (suffering) of Christ recently commemorated on Good Friday is a central feature of the faith. Even he cried out to God, "Why have you abandoned me?" That is the mental and emotional anguish of suffering.
Yet, as Teresa of Avila wrote in the midst of one of her great headaches, no pain lasts forever. If I think of this, can I prevent the negativity of suffering to take over my life? Can I really choose to avoid suffering?
If we are conscious of some element of hope, some sense that the pain will cease and that life will be worth living again, we are not fated to suffer the mental torment that seems quite other than physical pain.
This takes great courage and will power, to deflect attention from ourselves as an object of pity and to focus on something greater, as Samson does in Milton's poem, and thus to endure pain but not suffer. Whether we can do this alone, without external aid, is another question.