Why are some elements stable on their own while others are more stable in compounds?

The stability of elements is dependent on the outer most orbitals of their atoms. if they are full empty or half they are stable.  some elements like noble gases  have their outer most orbitals filled and are  therefore  stable on their own. 
some have unfilled outer orbitals  and  they attain stability by losing or gaining electrons to make the outer orbital full  which they do so by sharing them with another element in order to attain stability

Ido not understand.