Refer to figure.
When approaching a runway with an upslope, the pilot views it at an increased angle, causing him to assume that he/she is higher above the runway than they actually are. The angle looks the same as being too high to a flat runway. The pilot might then increase their rate of descent and land short of the runway.

• As a result, an upsloping runway can easily make the pilot believe that they are actually high on approach and have the IMPRESSION that they are going to overshoot the runway (land further inside the runway). To correct this perception, they may descent too low, with the risk of landing short of the runway. Trusting their flight instruments should counteract this illusion.

UPSLOPING RUNWAY
pilot's impression → approaching the runway higher, runway overshoot will occur
reality → approach is normal
correction based on pilot's impression → descent too low, undershoot the runway