I think this depends on what the actual challenge is that the person is experiencing, because that could be very different. Somebody who is experiencing grief with the world, whether a relative dies, whether they have lost half of their money in this economic crisis, whether their house burnt down, whatever - someone who is having that sort of problem in their normal life, it is going to be a challenge to generate joy with other people who are showing nice aspects, qualities and so on. That is going to be a challenge.
For someone else who is not having outside difficulties, then their challenges may be coming from other reasons, maybe coming from boredom as an example. You sit there and you are just bored, you can't have joy with anybody, because you don't want to be here. And you are having aversion to the retreat and this and that, you feel like going to the beach and so on. Again, there is a difficulty in having joy with others.
So dependent on what that challenge actually is, we have to pin point it, and if we can pin point it, then we can work towards letting it go. Remember the saying, "I felt bad that I had no shoes, until I met someone who had no feet." Let's say, you have just lost half of your money in the stock market or something similar to that, is life really that terrible? It can be a lot worse, right? Sometimes reflection on the simple fact that you are still very fortunate with what you have can help let go of grief coming from some of these material losses, to help let go of that challenge.
Say perhaps during the retreat you are bored, you would rather be at the beach, start reflecting on what that would actually mean for you if you actually went to the beach. What would it be like looking in the mirror tomorrow? What would it be like seeing somebody else from the retreat after the retreat is over at the beach? Reflect on the Dukkha of boredom as a mind state that brings rise to aversion and desire to want to be somewhere else. Bring forth energy for the practice by thinking, "Oh my gosh, I have only two more days here, I only have two more days, why am I thinking of the beach? Why am I bored and upset with what I have? I only have two more days here!" Okay, you may have to go away from the Sympathetic Joy meditation and get right into the how fortunate you are reflection.
If you are having trouble with the Sympathetic Joy, generating the joy, okay, move over to one of the other reflections for a while. Reflect on how fortunate you are, give yourself some other joy. Reflect on your good Kamma, chances are that you have much because you are here doing a meditation retreat! For all of you this is not your first retreat, this is not your second retreat. For those of you who have worked in the Dhamma for over 10 years, wow, fabulous, wild! Take some joy that you are on this path, take happiness that you are here! Great! So you may have to move away from the Sympathetic Joy, pick up some joy in another area and then come back to the Sympathetic Joy. Then it may not be so difficult.
So again, depending on what your challenge actually is, why you are having difficulties in the Sympathetic Joy, try to pin point that and then switch over to wise reflection to help let go of that challenge. Then when you are done, you may find that coming back to Sympathetic Joy is quite easy and in fact, if you are able to come back with a better frame of mind then who are you going to be happy about straight away? I hope you are going to be very happy about your teachers, who gave you the techniques, happy about the Buddha, who gave you the techniques. "Oh, my gosh I was depressed 10 minutes ago, I was depressed. I couldn't do this with beings. I didn't want to do it at all, but yes, I remember what they said, I did some how fortunate I am and yes, I am fortunate, I am fortunate! Wow, I'll go back now and do Sympathetic Joy on my teachers who are so wonderful who gave me that technique, on the Buddha, so wonderful, wow!"
Try it.