Explorer and Task Manager are both shells (along with their CLI sibling shells CMD and Powershell), but Task Manager is special in that Windows Logon is always

Explorer and Task Manager are both shells (along with their CLI sibling shells CMD and Powershell), but Task Manager is special in that Windows Logon is always actively monitoring for CTRL+ALT+DEL. Windows Logon is superior to all the shells as a core Windows subsystem in that it is the one that executes the shell (usually Explorer) on boot/login and can also execute Task Manager, in addition to its primary duties of tracking and securing user logins (hence the name). This means even if Explorer has completely froze or has crashed, you can always get to Task Manager via Windows Logon and then kill or execute another instance of Explorer (or CMD or Powershell!) or otherwise force reboot the system from Windows Logon.