When I am running Simulation, it is sometimes unclear what to do if it fails.
The Tcl console and the Vivado log might not contain sufficient information to debug the issue.
This Answer Record illustrates the immediate steps you can try if the Simulation fails.
As soon as the Simulation fails at any stage in Vivado Simulator, browse over to the Simulation Run directory which will be similar to the following:
(where sim_stage could be - behav, synth, or impl.)
There are three files which can be referred to for Errors.
Once you have found the errors in these files, you need to work towards fixing them.