CentOS Permissions – Group Needs –x on Parent Directory

I was trying to get the user nagios to have access a sub directory in another users home directory /home/alert/NagiosAlerts/.

I was going crazy setting permissions that should have been to high to get this work work (777 type stuff for testing) but was still getting permission denied doing simple touch tests. Started writing up a question here to ask and got linked to this dupe target which had the following in its answer:

The directory needs to be searchable to allow users to enter it or its subdirectory "project"

So that is what fixed my issue me as well. I change the group of the folder /home/alert and set the group permissions to --x and I am now able create files in /home/alert/NagiosAlerts/.

Why did I have to assign those rights in the parent directory /home/alert? I would have figured the rights in /home/alert/NagiosAlerts would have been fine?

If I touch /home/alert/NagiosAlert/file should it only matter about the permissions on NagiosAlert? Why would alert matter?