A 60-year-old woman or a 50-year-old politician can't possibly be as good as a 25-year-old commando-trained bodyguard at any kind of combat.
Agreed, yet not the point.
Queen Elizabeth has two military units guarding her at Buckingham Palace, both units no doubt filled with strikit, braw young men who eat snakes and can kill people with an emory board.
Not only that, but she has an entire dedicated police Special Operations Unit who probably drag their knuckles on the Persian carpets and practice leg-breaking 14 hours out of the day.
Three units of dedicated professionals and not a one of them was anywhere useful during the 12 minutes that Michael Fagin sat within arms reach of his target, cradling a jagged piece of glass.
What does it matter how good they are, if they aren't there?
You will always be there for you. You cannot be bribed away from your side. You will not be walking your corgis when the Poster Child for the Mildly Bewildered shows up in your bedroom and menaces you for twelve minutes. You will not be under a pile of Chilean Security Forces while you are undefended in a building 20 yards away.
This is why you are your best defense: You are the only person who will always be there for you.
Is this really so difficult to understand?