explain default behavior of ConfigureAwait()

what is the default behavior? will code continue to run on captured context by default or not?
> ...attempt to marshal...

Does that mean attempt may fail? Under what conditions?

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* Content: [Task.ConfigureAwait(Boolean) Method (System.Threading.Tasks)](https://docs.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.configureawait?f1url=https%3A%2F%2Fmsdn.microsoft.com%2Fquery%2Fdev15.query%3FappId%3DDev15IDEF1%26l%3DEN-US%26k%3Dk(System.Threading.Tasks.Task.ConfigureAwait)%3Bk(TargetFrameworkMoniker-.NETFramework%2CVersion%3Dv4.6.1)%3Bk(DevLang-csharp)%26rd%3Dtrue%26f%3D255%26MSPPError%3D-2147217396&view=netframework-4.7.2#feedback)
* Content Source: [xml/System.Threading.Tasks/Task.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Threading.Tasks/Task.xml)
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