The Holy Spirit had prevented them from preaching the word in the province of Asia at that time - Acts 16:6
It very important to know where God wants you to go, how to get there, and what to do once you have arrived
Bible does not say why God didn't want Paul and Silas in Asia at that time or how the Holy Spirit prevented them
The Holy Spirit faithfully guided Paul and Silas and the rest of those he had called to preach
The key is to be in tune with him by faithfully follwoing the guidance he has already made clear to you
When you follow the lead of the Holy Spirit, you can know without a doubt that you are right where he wants you