A little leak will sink a great ship.
More Portuguese Proverbs:
A small pack becomes a small pedler.Portuguese
Threads do not break for being fine, but for being gouty and ill-spun.
Portuguese
From the sweetest wine, the tartest vinegar.
Portuguese
The gentle calf sucks all the cows.
Portuguese
The tailor ill-dressed, the shoemaker ill-shod.
Portuguese
Another man's trade costs money.
Portuguese