Endurance is specified as the maximum number of writes (program/erase)cycles that can be performed on a byte or sector of data before a bit within that byte or sector will fail to read correctly. So it may happen that you program the chip and the verify proceudre tells you an error at address xxxx.

Some manufacturers specify their erase/write cycles only at room temperature and in the fine print this number goes much down than the stated value, with increased temperatures.