We may learn the wish of nature from the things in which we do not differ from one another: for instance, when your neighbour's slave has broken his cup, or anything else, we are ready to say forthwith, that is is one of the things which happen. You must know then that when your cup is also broken, you ought to think as you did when your neighbour's cup was broken.
I like the basic practicality of this advice. Step back from the situation, try and assess it from a more neutral point of view.
Transfer this relection to greater things also. Is another man's child or wife dead? There is no one who would not say, "This is an event incident to man". But when a man's own child or wife is dead, forthwith he calls out, "Woe to me, how wretched I am!". But we ought to remember how we feel when we hear that is has happened to others.
And now we step it up again. Apply the same neutral point of view to very upsetting events, like death. If it were someone else's loss, you would acknowledge that death is an inevitable part of life.
As a mental trick to play with yourself, this has some attraction. But it seems to me a little like parents telling thier children to stop complaining because there's kids starving in Africa. Pain and grief is an essentially personal phenomenon. It's certainly useful to try and take a broader view, and to pull yourself out of despair, but I'm not sure how effective this would be.
I do, however, find it quite effective for smaller things. If the kids are doing something typically horrendous, I try to think of what I would say about someone else's kids doing the same thing. It's really common to hear another parent chastising their kids and for me to think "hey, they're just a kid, give them a break". I don't use this practice as much as some of the other Stoic practices (like pre-visualisation, meditating on impermanence, and the dichotomy of control) but it is handy from time to time.