Praise the LORD, my soul! All that is within me, praise his holy name! Praise the LORD, my soul, and don’t forget all his benefits.
Twice in two verses David speaks to his own soul, and the repetition is the point. He is not describing a feeling that arrived. He is issuing an instruction to himself, because he knows what his soul does when it is left alone.
Then he tells it what to do: do not forget. Not “feel grateful”, and not “be more positive”. Remember. Gratitude in this psalm is an act of memory before it is ever an emotion, which is the only reason it can be commanded at all.
That is a genuinely practical thing to notice. Feelings cannot be ordered about, but attention can. You can decide what to bring to mind, and David is doing exactly that, out loud, where his own heart can hear him.
So the psalm is not asking whether you feel thankful today. It is asking what you have been choosing to remember.