It is in vain to cast nets in a river where there are no fish.
More Spanish Proverbs:
He who doubts nothing knows nothing.Spanish
Your cracked jug seems better to me than my sound one.
Spanish
You can't make pancakes without breaking eggs.
Spanish
He who promises incurs a debt.
Spanish
Wrinkles are the gravestones of love.
Spanish
He that eats the king's geese shall be choked with the feathers.
Spanish