Juan se justificó por el retraso diciendo que no le había sonado la alarma.Juan made excuses for himself for being late saying that the alarm didn't ring.
Cuando se te olvida algo, siempre te justificas diciendo que es mi culpa por no apuntarlo.When you forget something, you always justify yourself by saying that it's my fault for not writing it down.
Si te justificas lo que dices, es porque no tienes confianza en ti mismo.If you excuse yourself for what you say, it's because you're not confident in yourself.