The online dictionary defines common sense as "sound judgment in practical matters". It is "the basic level of practical knowledge and judgment that we all need to help us live in a reasonable and safe way." Unfortunately, not every normal person uses his common sense, as he should.
This post taken from Facebook should remind us of what common sense is all about:
If you open it, close it.
If you turn it on, turn it off.
If you spill it, clean it up.
If you drop it, pick it up.
If you dirty it, wash it.
If it doesn't belong to you, don't mess with it.
If you use the last of something, replace it.
If you are at somebody's home, respect it.
Only lazy people choose not to use common sense
and those are the ones that don't have consideration for others.