"It was difficult at the time," Vergne told the Spanish news agency EFE at an event for Toro Rosso sponsor Cepsa.
"But I think the winter break really helped me to think about everything. And I came to the conclusion that there is nothing wrong with being at Toro Rosso.
"It is the best option for me, and Red Bull has always made the best decisions for my career," said the 23-year-old.
"If they didn't choose me, it's because they didn't think I was ready yet. I need to work more on some specific areas. So I'm ready to do much better this year," Vergne added.
He said the Ricciardo situation forced him to take a philosophical view about his place in F1.
"You have two options," said Vergne. "The first is not to understand, and be angry. Or grieve. To think you're the best and they are wrong.
"The second option, which is what I choose, is to understand the reason for the decision and see the positive side. To work on all the aspects necessary for you to become a better driver. And be happy," he insisted.