I am reading in 3 Nephi 1 and 2, where the sign that the people had been intently watching for, finally came to pass. There was a day, a night, and a day of light. There were also many other signs and wonders in the heavens. It was an amazing experience and many people were converted to the gospel because of it. Then a few years passed and these same people began to be less and less astonished by the signs and wonders. They also started to talk themselves out of the great miracles they had already experienced.
I can relate to that. Some of the spiritual experiences I have had, I sometimes start to doubt, or tell myself it was just a coincidence or I was just imagining it.
This is why it is so important to write down in great detail any answers to prayers or other spiritual experiences that you have right away, when all the feelings and details are fresh in your mind. Then when the doubts start to creep in, you can go back and read what your feelings were at that time and gain strength again. It is also important to write them all down, so that you have more than 1 or 2 entries. You have a whole compilation of God's workings in your life and the more there are, the more convincing and irrefutable it becomes. Plus, it is important to feel the Spirit every day so that you have more than just a couple but it becomes part of you.
The other aspect of disbelieving for the Nephites and Lamanites at that time was that they were less and less astonished at the signs and miracles. How can we keep ourselves immune from feeling that way about the miracles in our lives? As I think about this and search my own heart, maybe this is where prayer and pondering comes in. The more we ponder about events and miracles and blessings in our lives, the more we keep the wonder and awe of it. Maybe keeping the Spirit with us helps us keep a spirit of gratitude, too. Had the people stopped being grateful for the signs and wonders?
Here is a scripture in Helaman (3:25) where the people did not become less astonished:
25 And so great was the prosperity of the church, and so many the blessings which were poured out upon the people, that even the high priests and the teachers were themselves astonished beyond measure.
From thinking about this, my conclusion is that if you are doing the things that keep the Spirit with you more often, that helps to keep you innoculated from talking yourself out of great experiences. The people that began to be less and less astonished were spending their energy talking themselves out of their experiences instead of turning to the Lord and continuing to add to their spiritual feelings.