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I'm sure this is a simple question. What I am referring to is disbelieving someone on Day 20 because they have lied every day previous to Day 20.

Another example is the boy who cried wolf. The 50th time he cries "Wolf!" nobody believes him.

As a matter of practicality it's perfectly reasonable to disbelieve someone on Day 20 or take the cry of "Wolf!" to be false, as we've established through experience that a person lies, and so we judge probabilities (unconsciously maybe) and choose not to believe them.

However I'm asking from a purely logical perspective. If a witness lies many times, their credibility is severely hurt, but it would technically be a fallacy to say their last testimony was a lie because:

1.The witness has lied ten times to 13 questions.

2.The witness has a tendency to lie.

3.The last statement from the witness is a lie. (invalid conclusion)

What comes to my mind is "hasty generalization". However "hasty generalization" is defined by Wikipedia as:

... a conclusion about all or many instances of a phenomenon that has
been reached on the basis of just one or just a few instances of that
phenomenon. It is an example of jumping to conclusions.
Faulty generalization (hasty)

Notice it says based on just one or just a few. I think this excludes my examples because the conclusion is not based on just one or few instances, but in some cases many, for example 30 instances.

I agree that it is "jumping to conclusions", but I feel there's a more accurate term for it. I feel there's a term for something like:

• Just because it's happened in the past (even every time) doesn't mean it'll happen now (even though the odds are in favor it happening).

Also, I know this is related to the problem of induction, (You don't know that the sun will rise tomorrow), but that's not a name of a fallacy.

I think I found something that comes close:

Appeal to probability (Wikipedia)

An appeal to probability (or appeal to possibility) is the logical fallacy of taking something for granted because it would probably be
the case (or might possibly be the case).

and

An appeal to probability argues that, because something probably will
happen, it is certain to happen.

The fallacy is an informal fallacy.

P1: X is probable.

P2: (Unstated) Anything which is probable, is certain.

C: X is certain.

The fallaciousness of this line of logic should be apparent from the second, unstated premise (P2), which seems and is blatantly false.

Appeal to Probability - Rational Wiki

I was thinking along the lines of appeal to history or something, not sure if such a term exists. I'd still appreciate any more suggestions.

This is not a fallacy, just the old problem of induction. A case of hasty generalisation would be to conclud that the witness tends to lie, if you have observed it two times in a row.