He who undertakes too many things at once seldom does any of them well.
More Dutch Proverbs:
No cross, no crown.Dutch
Looking down at one's nose.
Dutch
To hit the nail on the head.
Dutch
One swallow doesn't make summer.
Dutch
Young folk, silly folk; old folk, cold folk.
Dutch
He earns a farthing and has a penn'orth of thirst.
Dutch