Well, I for one have amnesia. All the times He has come through, and I still can get in a funk when things aren't going as I hoped. You'd think I'd learned, but I have to be taught again and again that I am Loved. I'm comforted, though, to know I'm not alone. In reading Psalms alone, I know that the psalmists also struggled, asking God where He was. I guess this comes with the whole "flesh" package. We get incredible pleasures, but we also get the struggle that comes with it.
If you have complete trust at all times, I'm ashamed to say I "covet" your trust. I've had seasons where I experienced it more than others, but in a moment of honesty, I can say that I don't more than I do. The Good News for me is that He sees me where I'm at, and Loves me all the same.
If we could fully grasp the promise He has made to us, I believe our lives would be a drift on a lazy river.