do it when they know vs do it when they are sure

Some examples from the web:

• These are employees who know more about their work than their bosses do. It is hard to tell people what to do and how to do it when they know more than we do ...
• Anyone can do it when they know how and have the proper support. Sadly, many people try a wide assortment of herbs, remedies, vitamins, and secret formulas ...
• Feb 3, 2016 ... And, why do they want to do it when they know that the fewest number of voters will decide the issue? They argue that registrars of voters ...
• Dec 4, 2015 ... People love doing burnouts and drifting at car shows. We only recommend folks do it when they know what they are doing. Besides, no amount ...

Some examples from the web:

• Jan 9, 2015 ... I think fur is still worn amongst the really wealthy - they just do it when they are sure there is not going to be a camera around.. Read more ...
• Jul 15, 2010 ... Many people will attack someone for "insulting" their wife or girlfriend, but it seems to me that they only do it when they are sure they can "win".
• Nov 4, 2014 ... Many people will attack someone for "insulting" their wife or girlfriend, but it seems to me that they only do it when they are sure they can "win".
• Nov 20, 2012 ... "They only do it when they are sure that they are wanting to proceed with a development project like this," he said. "The cost for these projects ...