Is it right that for our brain to memorize something it needs to be repeated 3 times ?

Not necessarily: Memory skills vary from person to person. They also vary with the state of restfulness, health, environment and nutrition. A well rested and fed person, who is well and in a safe place can perform better than one who is not. Some have better abilities with memory than others and can see or hear something once and have it forever.Some will review it dozens of times before they have it.