We are more often treacherous through weakness than through calculation. -Francois De La Rochefoucauld
I interpret this quote as saying that being weak causes more damage than actually taking a challenge. Similar to the saying "you can't win if you don't try". Like solving a problem. It is more detrimental for one to give up than to have actually attempted at solving the problem.
A man with one watch knows what time it is; a man with two watches is never quite sure. -Lee Segall
This just means that someone should focus on one thing t a time. Like in work or school. Taking on more than one task at the same time can cause confusion.