Usages of lamentar
Lo lamento, ayer iba a viajar, pero choqué el carro.
I am sorry, I was going to travel yesterday, but I crashed the car.
Lamento el problema, iba a enviarte una disculpa.
I am sorry about the problem, I was going to send you an apology.
Él tenía un gran potencial; lamenté que lo hubiera desperdiciado.
He had a great potential; I regretted that he had wasted it.
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