Mary Poppins.
'A spoonful of sugar helps the medicine go down'

Assumingly, I always thought that the spoonful of sugar was to help swallow a nasty dose of remedy. I'm thinking about how 'sandwiching' a constructive feedback between two generous compliments is pretty much par for the course at the moment. Say something positive, slip in the room for improvement tip and and add another positive something.
 That is one kind of spoonful of sugar. 
 Only problem is - it implies that the construcive criticism is something uncomfortable and something to be endured.  When really it is just our conditioning and inner beliefs of not being good enough that make it so.  Constructive feedback really could be 'medicine' designed to heal, help and nourish us to a better state of being. Perhaps if it is offered from a good intention, receive it so!