grandchild of someone’s first cousin / cousin of someone’s grandparent / grandcousin

One is cautious if one has been hurt in the past.

Alternative form of measure twice and cut once

(carpentry, literally) One should double-check one's measurements for accuracy before cutting a piece of wood; otherwise it may be necessary to cut again, wasting time and material.

plural of first cousin twice removed

Buying a cheap but inferior product is a false economy since it will need replacement.

Synonym of once a man, twice a child

(rare) A woman is born as a child, later enters adulthood, and consequently enters old age, when her body and mind start to deteriorate to the point where she can no longer care for herself.

A man is born as a child, grows to adulthood, and consequently enters old age, when he deteriorates and reverts to a childish state.

Opportune times seldom appear again.