Musar zu Tehillim 118:16

In other words, such people penetrate to one half of the ribotayim mentioned in Psalms 68,18. This is why the verse in Psalms 91,7 is quoted, since it speaks of revavah =ten thousand, instead of rivotayim, twenty thousand. The meaning of Kohelet 6,6, in which even twice a lifetime of one thousand years is described as ultimately futile, is that unless one achieves רבבה, the level of עולם הבריאה, one has failed to achieve one's goal, i.e. half the “full yud.”