Cron+ settings. * vs ? help please

I'm trying to keep things separate.

I've been pointed in the direction of cron+ and in the config line I saw this:

0 30 6 * * ? *

Digging I find this:

* Asterisks indicate that the cron expression matches for all values of the field. For example, "*" in the minute field means every minute

? Question marks are used to specify 'no specific value' and is allowed for the day-of-month and day-of-week fields. It is used instead of the asterisk (*) for leaving either day-of-month or day-of-week blank.

(My hand is up)
What's the difference?
I see the words, but their meaning is lost for me.

Free Online Cron Expression Generator and Describer - for output

and for explanation Scheduling tasks with Cron - Raspberry Pi Documentation

* means every.

? means don't care.

So when you have 10 in day-of-month AND * in day-of-week they contradict each other. Do you want the 10th? or every day of the week? It's a contradiction.

So in essence, the ? Says "I am not relevant, use the other values to make sense of the Cron schedule"