Daniel Ricciardo has said that it is former teammate Sebastian Vettel's unbridled focus on F1 that leads to his obvious "frustration".
After Vettel's run of four straight titles at Red Bull, the pair were teammates in 2014 before the German moved to Ferrari.
When asked by the Sydney Morning Herald about Vettel's clear signs of frustration in 2016, Ricciardo said that the quadruple world champion is "pretty unique".
"He is someone who lives and breathes it more than most. It seems like the majority of his life is the sport and being world champion," he said.
"That is not a bad thing, but when things are not going as you want, those frustrating things can build up because that is what you are really looking at in life.
"I think he had a dream with Red Bull, one of the best runs in history. So I think he probably expected to have a dream run with Ferrari and it hasn't come as soon as he would have liked.
"He is super talented but I think sometimes he is his own worst enemy in terms of that frustration side of things. When he cools down, he's cool."
Ricciardo and Vettel finished third and fourth respectively in the 2016 driver rankings.
