If you want to do a fun experiment, try and watch the pain in two subjects faces. One who has never used predictive text trying to use it for the first time, and one who has used it for years and is trying to use an old phone without it. Now imagine a scenario where every predictive text implementation had tailored itself to the user.
On the other hand when you're trying to do some specific task you already know in most cases exactly what you want to happen, so if it does something else then that is very frustrating.
OTOH when we have smaller and more focused collections of information such as programming documentation or catalogues of similar products we tend to find it easier to navigate with categorical listings or simpler search algorithms.