Explain the saying "Tedium is the worst pain."

"Tedium is the worst pain." p. 138 Grendel explains how boredom is the worse kind of pain. This constant boredom intensifies in chapter ten and only makes Grendel more anxious for something to happen. This statement is almost ironic because Grendel claims nothing is happening and all is boring, yet he still finds himself expecting something big to happen soon. Please check out my source link for this excerpt.