After a highly successful (first) missionary journey Paul and his companions wanted to preach the word in Asia, but the Holy Spirit kept them from doing this. They tried to go to Bithynia, "but the Spirit of Jesus would not allow them". Finally they ended up in the seaside town of Troas, probably confused and frustrated by doors closing on every missionary opportunity he could see. It became the pattern of Paul's life. We should really rename Murphy's Law to Paul's Law.
He wanted to go to Corinth to sort out a church that was in an absolute mess, but he could not - so he wrote them a letter. That letter was taken so badly by the church that it took two further letters (of which we have one) and a lot of tears to clear the air and mend the relationship. He wanted to go to Philippi to personally thank them for their overwhelming and ongoing support of his ministry from "the early days", but he was sitting in prison - so he had to write a letter. He longed to see the church in Rome and "planned many times to come to you (but have been prevented from doing so)" - he had to put his teaching to them in a letter. When he finally got to Rome, it was in chains, and he could not leave his house to meet the church. He wanted so desperately to see "my dear son" Timothy, and had "hope to come to you soon", but it didn't happen ... instead he was in prison, again, and he knew that this was the end of the road - his final words to his "true son in the faith" had to be in a letter.
For Paul, it seems, it was always Plan B. Or was it? It was in Troas that he saw the vision convincing him to take the gospel to Europe. Imagine how thin the New Testament would have been without Paul's letters, all of which were written because he couldn't go in person! What would the world have been without his teachings, his insights into every aspect of human life?
It was never Plan B. Paul might not have known it then, but looking back with the hindsight of twenty centuries it is clear that everything happened according to The Plan. We may not always see The Plan, but God does. We just need to walk the path He opens to us.