To have ambition is a self-inflicted disadvantage (3,4)
I believe the answer is:
own goal
I believe this is a double definition.
'to have ambition' is the first definition.
(I've seen this before)
'self-inflicted disadvantage' is the second definition.
(I've seen this before)
'is a' acts as a link.
(Other definitions for own goal that I've seen before include "Self-damaging mistake" , "move that backfired?" , "or occasionally with it?" , "Unintentional self-inflicted harm" , "A self-inflicted injury, from soccer" .)