и всегда в контексте "не встречал(а)" вопрос - а был ли у вас fair chance это встретить? а то я вот например сусликов в жизни не встречал .. но это же не значит, что их нет! (просто не хожу по местам богатым сусликами)

Отполз, поджавши хвост.

Grammarians think of questions as being transformed forms of statements.
So, for example, the statement She is pretty can be made into a question by inverting the subject (she) and verb (is) to form Is she pretty?

Likewise the negative questions come from a corresponding negative statement.

She is not pretty.

In modern English the transformation of a negative statement into a question can be done in two ways:

1 Invert subject and verb.

Is she not pretty?
This gives a rather formal, even stilted sounding form, but is fine grammatically.

2. First contract the verb and the negative: is not > isn't
She isn't pretty.
Then invert the subject and the contraction.
Isn't she pretty?

There is no transformational rule (in modern English) that allows the movement of the negative not to the left across the subject except as a negative contraction connected to the verb. For this reason, Is not she pretty cannot be generated as a grammatical sentence (in modern English). The not must be expressed as an attached n't or it can't be inverted with a subject.

So, strange as it may seem, even though in most circumstances isn't is the same as is not, the two expressions are not absolute grammatical equivalents. They undergo transformations in different ways when forming questions.