I understand your confusion. You must realize that experience has multiple meanings. It may refer to single encounters or to collective wisdom. the meanings are as follows :
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1. a particular instance of personally encountering or undergoing something: My encounter with the bear in the woods was a frightening experience.
2. the process or fact of personally observing, encountering, or undergoing something: business experience.
3. the observing, encountering, or undergoing of things generally as they occur in the course of time: to learn from experience; the range of human experience.
4. knowledge or practical wisdom gained from what one has observed, encountered, or undergone: a man of experience.
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when we use Experience to mean the 1st meaning given above, we can use the plural form. e.g. I have had many bad experiences of encounter with bears in the woods.