Threads do not break for being fine, but for being gouty and ill-spun.
More Portuguese Proverbs:
Thinking is not knowing.
Portuguese
You can't make a silk purse out of a sow's ear.
Portuguese
By going gains the mill, and not by standing still.
Portuguese
Give a loaf, and beg a shive.
Portuguese
If you would grow poor without perceiving it, employ workmen and go to sleep.
Portuguese