I’ve always wondered what the goal of this was and why Japan became isolated, It’s hard for me to think that not allowing trade with other countries could be beneficial to japans success. What this a good foreign policy choice for japan? What was the goal of isolationism?
They never banned trade. They banned Christian missionaries, and then forced all trade ships to go through one port (Nagasaki) to make it easier for the authorities because the missionaries won't stop trying to sneak into the country. The act didn't even effect trade volume.
See here for more detail.