Trying to get the Select or select all options when placing cursor on a word and holding it down

When I want to select/select all, I usually hold down the cursor on a word for a second, and it gives me the option, but not all the time. Am I doing something wrong? Yes, I am running the most current version of iOS for ipad and iphone. It has actually been happening for a while, but the inconsistency is starting to bug me.