"Letting go" is something that can't be forced.

IIRC, the author doesn't use the phrase "letting go" anywhere in the book. He operationalizes all the terms/skills/states he talks about like differentiating between continuity of attention and sharpness of attention. I think the goal's he's talking about are very specific/operationalized.

I have not said something about "really wanting to" being bad.

My bad. That was a bit of a straw man on my part.

The problem is attachment. If you have once a really great experience meditating and then get attached to the idea of recreating that experience you usually don't get anywhere.

The author addresses that specific concern:

A warning is inorder here. It is very important not to sacrifice the development offull-minded awareness for sake of rapid progress in concentration. Todo so will lead to the development of concentration with dullness.This will produce very pleasurable meditative states that are dead-ends in themselves, leaving the meditator without the capacity for full-minded awareness necessary for completing the 10 stages of this method.

Overall, I think the first section of the book is skippable. You can use what's useful to you and leave the rest.