I am going to look deeper at this, because I think there is something missing in the question. Let's go to somebody like Christopher Reeve. Most of you know about the American actor, he played Superman, yet then he became paralyzed from the neck down. Seemingly you can't see something he did in this particular life that should cause so much Dukkha. So, when I read, "Dukkha may manifest at any moment," I think, well, yeah, there is someone who's Dukkha manifested, yet there didn't seem to be an actual cause in this lifetime.
Buddhism will say it is from past lifetimes. So, can he be responsible for his own Dukkha? Can he actually be responsible for that Dukkha? As far as who he is in this life, he has to accept the Dukkha, but was he responsible for it? Buddhism will say, well no, who he is today, who he is in this life is not responsible for it. But who he used to be was responsible for it. Any unpleasant experiences that come, any Dukkha, especially of the nature in which we can't see the causes in this life, then Buddhism says it is from a past cause, a past life.
So it can be helpful to consider that every time you do good Kamma today, you are doing something for somebody else. Now you may have an instant result, you get it really quick and you know it is good Kamma, you get benefit, joy, whatever. Sometimes you don't get it quickly, yet somewhere down the line you will get your gift, the person who you will be will receive it.
Rosemary and I often refer to ourselves as people who are not only doing things now, but we are taking care of who we are going to be.
The Dukkha that comes to us now, we may not be responsible as to our actions, speech and thoughts in this life, but we still have to bear it, we still have to take it, we still have to deal with it. And how you react to it now, that is your responsibility. Something unpleasant comes to you now, maybe from a past life, as we assume with Christopher Reeve, then he still has to deal with it now, and how he deals with it with it now that is was his responsibility. If you have read his autobiography books, he refers occasionally to other people who became quadriplegic who gave up, but he didn't give up. He almost gave up in the beginning they say, he was almost ready to say, "Take me off the life support machine so I can die." But no, his wife encouraged him to continue and he is doing lots of good with her and others helping.
He is very active even though from the neck down he is not much. [he was still alive at the time of this question] But as to doing good Kamma now, he is doing a lot more good Kamma than maybe 99% of the people on the planet. He is very active raising money for other quadriplegics, for research into the spine and all sorts of things. He is doing a lot of good Kamma but his physical body is worse than everyone here and worse then 99% of people, yet he is doing better Kamma than most.
So, this is something to look at. You may not be able to see how you are responsible for the Kamma that comes to you but you are responsible in the moment for how you react to it.