Example of Octet-Deficient Molecules

Boron trifluoride BF₃

But BF₃ reacts very energetically with molecules such as water and ammonia that have available electron pairs (lone pairs).  This indicates that BF₃ is electron-deficient.  Experimental evidence also indicates there is no double bond in BF₃ (fluorine never forms double bonds.)  Furthermore, a positive formal charge on F is extremely disfavored.  So placing only six electrons around the boron is more correct.  At least it assigns zero formal charge to all atoms.