Chances are, if you have an iOS device of some sort, you have apps. And if you have apps, chances are that you have too many of them. They start to get lost in the crowd. I find that, for myself, once I get past the first couple of app pages, I might as well tap at random for all I can find the app I need.
There are ways to launch the app you want, of course. You can bring up the multitasking bar with a double tap on the Home button, and swipe through a list of the most recently running apps. If you haven’t used the app you’re looking for in a while, though, it may not be there.
You can also use the Spotlight search function. When on the first page of apps, either swipe left or tap the Home button once. Type the name of the app you’re searching for into the field there and you’ll see that hidden app. Tap on it to launch. But you’ll have to do that every time. Spotlight won’t tell you WHERE that app resides.