While will Undo the last action and will Redo the last Undo operation, sometimes we need to go back a long way.
We can target a more precise history point by accessing the history list:
We can now click on one specific action and see what happens when that action is undone. If we change our minds, we just reaccess the list and choose a new action to undo instead. The Undo only becomes final when you perform a further operation after which all actions after that are irrevocably removed.
Unless you are very short of RAM, adjust the number of undo steps to 256 in the preferences panel: