Also, let slip or slide by; let slide. Miss an opportunity; waste time. For example, We forgot to buy a ticket and let our big chance slip by, or He let the whole day slide by. The first term dates from the mid-1500s, the variant from the late 1500s.
Also, let slip out. Reveal something, usually inadvertently, as in He let it slip out that he had applied for the vacant position. [Mid-1800s]
let slip through one's fingers. Fail to seize an opportunity, as in We could have won the trophy but we let it slip through our fingers. [First half of 1600s]