Here's a riddle by Francis Bacon --

"For occasion turneth a bald noddle, after she hath presented her locks in front, and no hold taken." 

Bacon is here referencing a common saying and imagery of his time, personifying opportunity (occasion) as having hair at the front and being bald at the back. 

This emphasizes that if one does not seize an opportunity when it presents itself (by its forelock), 

it quickly passes by, and there is nothing to grasp once it is gone.