I am not able to recover my lost files. Why?

This completely depends on data loss situation and the drive usage after the data loss. Few factors do affect the recovery chances and some of them are complexity of the data loss, whether the respective drive was used to save data after the data loss situation, the drive might be severely fragmented.

If the drive from which you are trying to recover lost file has faced any of these factors, then the lost files cannot be recovered.  

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