This sounds like it might be helpful for people who encountered the same problem as I did in trying to apply DavidM’s method, namely knowing what to expect (or whether to expect anything) as a result of performing the first-phase meditative exercises: http://www.urbandharma.org/udharma7/enterjhana.html
It would seem that having a purpose or expecting a result could be the very thing that prevents you from getting that result, in certain phases or aspects of meditation.
Actually, the Expectancy (probability of success) component is not that simple: you don’t just maximize it to maximize motivation. As Robert Sapolsky shows in “The Uniqueness of Humans” (https://www.youtube.com/watch?v=hrCVu25wQ5s), motivation is proportional to the dopamin spike you get when you start to consider performing a task, and the dopamin spike is highest the closer your estimated probability of success is to (something like) 50%! The amount of dopamin produced when you consider starting a task that you have 25% or 75% chances of succeeding at will be significantly lower than for the 50%-chance task. So it’s not that you need to be certain about your success, it’s that you need to be pleasantly challenged, somewhere midway between “I’m so gonna fail” and “I’m so sure I can do this I find it absolutely boring” (though this sweet spot may not be at exactly 50% for everyone).