Where the river is deepest it makes least noise.

Related:

• Knowledge is like a river ... The deeper it is,
  the less noise it makes...
• One coin in the money box makes more noise than when
  it is full. Arab...
• It's the empty can that makes the most
  noise...
• Italian Proverb She who is silent
  consents...
• Donna pelosa, donna virtuosa. --
  Italian...
• He who is not impatient is not in love. --
  Italian...
• It is not enough to aim; you must hit. --
  Italian...
• Small children, small problems. --
  Italian...
• Speak of the devil and he appears. --
  Italian...