Breakpoints are the cornerstone of debugging in UE4 blueprints. They allow you stop the execution of the blueprint and observe that values of certain variables at the time execution was halted. For your case, right click on the Possess node after the Set Closest Actor node and then click on Toggle Breakpoint. A red circle will show up on the node. Then run your game and click the right mouse button to execute that section of code. When it hits the breakpoint, your game will stop and you will be able to see the value of Closest Actor by putting your cursor over the Set Closest Actor Node. This will tell us two important things. First it will tell us that it got to the Possess Node. You would be surprised how many times a BP doesn’t work because it doesn’t even try to run the code you think it is running. Second it will tell us which Character you are going to try to Possess. A possible issue with your BP is that there are no character to possess, in which case the Possess node isn’t going to possess anything.