When you allow the debugger to step into external assembly code (that is, load debug symbols for other assemblies), Visual Studio may "pause" or behave like a breakpoint in the code of those assemblies, especially when TraceInternal.Fail() is called from within a Trace.Fail() method.

If you do not want this behavior to occur, in Visual Studio, go to Tools > Options > Debugging > General and make sure the Enable Just My Code option is checked. When this option is enabled, the debugger will only pause in your own code and will not step into the code of system assemblies.