Why did my glass piece break when i set it down on the counter? Even though it has survived more severe falls

Each time a piece of glass makes a hit, that hit can cause stress in the glass that you might not be able to see.  As the stress builds up, this can cause the glass to break.

Just a scratch in glass can cause a nasty stress in the glass making that a weak point for potential breakage in the future.

Also, the angle of the hit has a huge role in how it will affect the glass.  Glass