[Visualforce / Tip] Always add a <apex:pagemessages/> tag

Always add <apex:pagemessages/> at the beginning of your VF page to see if there are errors in loading/submitting VF page.
If something underneath the Visuarlfoce is wrong, you don't see anything (no clear log at least)!

I was using the automatic SOQL generation of the "Object__c" standard controller, and to do this I usually use (well, I used to do it in the past, now I only use a series of "{!field}" in a hidden <apex:outputPannel>):

     <apex:inputHidden value="{!Object__c.CreatedDate}" />
     <apex:commandButton value="Do something" action="{!doSomething}"/>

This is clearly a blasphemy,because you cannot set with input hidden a "created date" field, but as I hadn't wrote this piece of code myself, I didn't see it immediatly.

Result was that commandLink/ButtonLink was not working, no log provided (exception made for the page load's initialization debug log), everithing I did made the button simply reloading the page without a real postback.

Using a simple <apex:pagemessages/> I saw the error and manage to know what was the problem.