All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

As regards your question about Allaah's Decree whether it is all good, the answer is that all Allaah's Decree and Predestination are based on His Wisdom and Knowledge, Allaah Says (which means): {And you do not will except that Allaah wills. Indeed, Allaah is ever Knowing and Wise.}[Quran 76:30]. So Allaah's Will comes from His Knowledge and Wisdom. Since this is the case, all Allaah's Decree and Predestination are good because it is based on His Wisdom and Knowledge. It is for this reason that the Prophet used to say in his opening supplication of the prayer: "And all the good is in Your Hands and evil is not attributed to You." Ibn Abdul-'Izz said about the interpretation of the above: "Evil is not attributed to You" means that Allaah does not create a pure evil, rather, there is good in everything that Allaah creates, but there could be some bad in this good for some people, and this is a partial evil. As regards the pure and absolute evil, Allaah is high above creating it; and this is the kind of evil that is not attributed to Him." Therefore, if someone is about to travel and his trip is cancelled, as mentioned in the question, then it is Allaah Who predestined it and there is good in it; it could be that Allaah has repelled an evil from the traveller, an evil that this traveller does not know, or that He has brought for him some goodness that he does not know as well. What is important is that one should know that the Decree and Predestination are from Allaah and they are based on His Knowledge and Wisdom whether they brought some good for him and whether he knows the wisdom thereof. Allaah Says (which means): {Allaah knows but you do not know.}[Quran 2: 216]. In addition to this, if a believer believes in Allaah's Decree and Predestination and knows that anything that happens to him is predestined and decreed by Allaah, and acts according to this belief, being graceful to Allaah and patient, then this is of the greatest goodness. Indeed the Prophet said: "How wonderful is the case of a believer for there is good in every affair of his and this is not the case with anyone else except the believer. If he is blessed with prosperity, he thanks Allaah, thus there is a good for him in it, and if he is afflicted, he endures it patiently and there is good for him in that." [Muslim] So there is good for a believer in the Predestination and Decree of Allaah in all cases.   

Allaah Knows best.