I disagree. One can be and usually is gradually brainwashed, often since birth and never know that one is being brainwashed. Brainwashed parents will unwittingly put their children into this state. We can even brainwash ourselves insofar that we refuse to accept reality and live in an unrealistic optimistic state.
Most of us are brainwashed since birth. We learn it from our brainwashed parents first, then it continues in school, in church, in the institutions of higher learning and in the Media, of course. Most brainwashing is really quite subtle and involves a conditioning process.