My explanation is that the number of things that have worked before is so overwhelmingly great that it would be impossible for the conscious part of our brain to remain aware of them. The capacity of our conscious attention is quite limited. We mostly use it to focus on what is really important and urgent in the present. The large majority of what we have done well before sinks, as it were, into the basements of our minds where it is not easily accessible. When we are suddenly confronted with a problem we may not have a clue about how to solve it. We may think we are not capable of solving it because we don't see what we can do. But we often underestimate ourselves. As progress-focused practice often shows, we turn out to have far more solutions than we consciously know.
What progress-focused coaches do is to focus the deliberate attention of clients to find out what has worked well in relation to the specific problem (or goal) at hand. A metaphor to describe what happens in progress-focused coaching is that of a client who is searching for solutions in a darkened room. The client is shining his flashlight into one corner of the room only and finds no solutions there. This corner is the corner of the present in which the problem is unsolved. The client concludes that, apparently, there are no solutions. The progress-focused coach subtly suggests - mostly through questions- to focus the flashlight in some other directions. Then, gradually, the client starts to discover some other corners in the room. In one of these corners past successes are found. In another corner clear descriptions of the preferred future are found. Slowly but surely, solutions become apparent.
When we help clients shine a light on what has worked well, they begin to see what is there, which is often much more than they had hoped to find.