"Any form whatsoever" can mean the computer that's in front of you now, the money you spent yesterday, the breakfast you get tomorrow. If you regard it as belonging to you, you're still caught up in clinging.
And how do we not regard these forms as mine? Simply by understanding them. Anything that arises also passes away without our control. It is not me, it is not mine.
Elements arise and fall. Colors arise and fall. There is one moment of sense impression, then another, and another, and so on. They just arise. They just keep arising. Tell me, does the next moment of seeing arise because you choose it to or does it just arise? It simply arises. There are conditions for it's arising.
Thoughts just arise. They too are to be seen as "not me, not myself, not belonging to me". We see a photo. A thought arises about that photo that is connected to that photo. The conditions were there for it to arise: there was a visual object, contact was made, we have a sense organ that apprehends the visual object, so then a thought arose in the chitta, it was colored about that object by past impressions left in the chitta that arose based on their own conditions. The next time we think it may be conditioned by that experience we just had with the photo. Then sound arises, touch, and so on. There are reactions to these based on what is stored in the chitta.
It is an illusion. We do not have control. Making decisions is just a conditioned reaction as well.
Why? Because all dhammas are anatta. It is so simple. Yet, the habitual pattern of seeing things as self, of having a self, of having some sort of control is so deep from so many lifetimes of delusion.
We need wisdom on the level of understanding, then the ground is set for wisdom on the basis of penetrating the anatta aspect of arising dhammas is set to happen with objects as they arise, naturally, proper conditions arising for those objects such as color, sound, and so on to arise.