what is does a fortiori possible mean?

The following from:
https://www.gotquestions.org/a-priori-posteriori-fortiori.html
may help:

[i][b]A much less-commonly used term, a fortiori, describes something related to a priori knowledge but not exactly the same. The term a fortiori means “from the stronger,” and it refers to arguments that seek to prove a “smaller” point by appealing to an already-proven “larger” point. For instance, if a man says he can afford to spend $100, we assume he can afford to spend $10. If drinking one sip of a liquid is fatal, we assume drinking an entire cup is also fatal. If a man can hold his breath underwater for three minutes, we assume he’s able to hold his breath for one minute. If it’s considered a sin to punch someone, we assume stabbing him would also be sinful.

When we argue a specific point based on some larger or broader established idea, we are using a fortiori arguments. In common dialogue, we often use phrases such as “even more so” or “all the more.” This is, in general terms, an appeal to a fortiori logic, and the examples given might all be framed using that kind of language.

Technically speaking, a fortiori arguments are not ironclad to the same extent as truly a priori statements. In the prior examples, if the man in question had been given a signed check for $100 by a friend, he might only be able to spend exactly $100. In other words, it’s logically possible that he can “afford” to spend $100, but not $10, since he has no other money. So, while a fortiori arguments are reasonable, they are not logically absolute, so they are not truly a priori[/b][/i]

So based on the examples given:
If a man can afford to spend $100 then we assume he can afford to spend $10 is a fortiori possible.
If a man can afford to spend $100 then it is not 'a fortiori' possible that he can afford to spend greater than $100