The 26-year-old looked to be on his way out of Vicente Calderon following a series of injuries and loan moves, but is now a key member of the Argentine's squad
The Brazilian forward joined the club in 2010 but struggled for regular first team football, following a number of injuries, and spent the second half of last season on loan at Rayo Vallecano.
His form there propelled him back into Simeone's plans and he has thanked the Argentine for helping him return to his best.
"He told me he didn't have any friends in the squad, that whoever is better at the moment will play," he told AS.
"Whoever fights and gives everything will play. This gave me confidence that I had made the right decision to stay."
The 26-year-old has admitted he made mistakes earlier in his Atletico career, but says he has matured and learnt his lessons from the past.
"In life you learn from your errors, it would have been stupid of me not to have learnt from my errors," he explained.
"Not only as a player, but as a person. It's not been easy for me, with loans, operations, and rehabilitation, but life is a constant lesson we must learn from.
"Sometimes you don't have the same touch of inspiration as other days, but if I put in the effort, the hard work, if I give everything, I will reap the rewards. That is my mentality."