on what the Buddha taught
Anicca is often translated as impermanence.
You may have seen it in something that roughly goes like this:
Is form permanent or impermanent? Impermanent.
What is impermanent is that sufferable or happy? Sufferable.
Is of that sound to say 'this is me, this I am, this is myself'? It isn't.
The answer to the last question might be clear when it is seen that if form were self it would be possible to have of your form 'be like this and not like that' and thus it wouldn't be liable to suffering (SN22.59). And regarding the first question you might find a reason to give the same answer as the first one. But for the second question the answer is then not evident at all. It must be that the meaning of anicca has something to do with it. The dictionary does give some options, so let's see. Let's start by making two groups. Group A for impermanence and kindred words, and group B for some other options.
Now for group A. Many people already know that form, etc. are not permanent. And what is their answer to this? Live life to its fullest! Enjoy while it lasts! The negatives and the positives are seen as inevitable parts of life and one can only try to get as much of the positives as one can. And if they take this statement of things being impermanent to heart, then they would also be able to accept that there is no magical potion to make them everlasting, nor such a favour to expect from a deity, or from scientists finding a scientific solution, they won't have to worry about any possibility for those things to exist. So they can focus with an even lesser reserve to living their life to its fullest. The effect this impermanence has is not one that makes people want to turn away. Thus is the answer to the second question not evident at all, and this means that the sequence has become invalid.
Then for group B, let me explain it like this: Suppose you have in another country a family vacation home where you and your family are staying. It is entirely made out of untreated wood. So if someone tells you it is impermanent you can agree to it, even if you don't know what the question exactly was about. Was it that the house won't survive for generations, or the current woodworms? Or was it that you can't stay there long-term? It is after all not a permanent residence. In any case, you can agree. And so you give a thumbs up, especially since building a vacation home is part of your family's fun. So all is good. But suppose this person was an official and your reaction was not what he expected. Figuring his english wasn't good enough he signs his colleague to help him out. And you learn that apparently, because of old minings and the recent earthquakes, the area has become very unstable and evacuation is in order. Would you now enjoy your stay like there is no tomorrow or would you take your loved ones and evacuate? Why? Because the liability to suffering is evident. It doesn't matter to much if the experience is an enjoyable one, preferable it is but, safety first! Unstable for anicca is found in the dictionary, and with it the question 'What is impermanent is that sufferable or happy?' is evident.
But it might be that the question 'Is form stable or unstable?' may seem as if it has a similar problem, that the answer is not evident; why not an answer like 'Sometimes stable, sometimes unstable'? If so, what do you think, would it be better to validate something as stable at face value or after investigation? So then, what makes it that f.i. a house is unstable? What you'll arrive at is its support. And thus we need to look at the stableness of that support. Anything that is supported, carried, by something which isn't stable, is not stable either. Now form is inclined. And what are the characteristics of the inclined? Arising, passing and the alteration when stood are known. And as these characteristics are inclined too, so they too arise... etc. (AN3.47). Looking at it this way we can now see why it must collapse; this whole structure is unstable. And perhaps you might have heard something like 'subject to change, thus suffering', which too is not so evident? The pāḷi talks about change-for-the-worse (vipariṇāma) and then it is evident. Such a change in structure is per definition the deterioration; it can't lead to stableness.
So, the difference between these groups is not so innocent. Group A is about existence through time, about views connect with eternalism and nihilism; a container of wrong views. While group B is atemporal, structural, about depended-co-arising.
'What is unstable is therefor sufferable, what is sufferable is therefor not self and is thus not to be regarded as 'this is me, this I am, this is my self'.'
Anicca (adj.) unstable.