I don’t think that anything Hashem sends us can be not for the good, but sometimes Hashem gives us things or has us experience things that are “good for us” but it is hard to see the good. Let’s say, for example, the loss of a friendship when one party moves far away. Now you might think that it’s not good for you, who wants to lose a friend. But, Hashem knows that it is good for you, because maybe you were too dependent on that friendship or whatever, and now without it you will develop more independence, more leadership skills, new friends, etc, that you might not have done had you had that friend close by. Was it painful? Yes. Was it good? It was hard to see in the beginning, but maybe with hindsight the person might appreciate that it was in fact good for him even though he did not think so in the beginning or even in the process of reaching the final goal.
I think it is helpful to ask Hashem to give you what is good for you and for it to be sweet and that you should be able to see the good (so that it is obvious that it is good and you’re not left wondering).