Steps such as Global Context, Data conections and LUIS rely on external services which may fail when calling them for numerous reasons. In such cases we would like to handle the fail case logic in a flow that is separate from the successful path.
For this reason, steps that may fail, expose a "fail" output node. This node will allow to branch from this step to a step that handle the fail case logic.
If there is no "fail case" connected, the flow of the scenario will continue to the success node even in the case the step has failed.
If you have not connected your scneario to the "fail case" node, it is recommended to check for a succesful or failed outcome of the step to apply the correct logic to handle the failure.