一寸先は闇（いっすん さきは やみ） 'You never know what tomorrow will bring.'

「一寸先は闇」（いっすん さきは やみ） tells us that we do not know what will happen in the future, even tomorrow.

「一寸」（いっすん） is about three centimeters. However, this saying does not speak of distance but time actually.

「闇」（やみ） is darkness, which implies ignorance.

This saying has been used since the 16th century.