For everyone who has been born of God overcomes the world. John writes this as a fact, not as a command. You do not overcome through effort but because you are born of God. That is your starting point in the New Covenant.
You may feel strong one day and shaky the next. But your overcomer status does not depend on your daily condition, it depends on your origin: you are from God. This is righteousness as a gift, not as a result of your performance.
Today you may live as who you are: an overcomer by birth, not by battle.