Onana is on-loan at Trabzonspor this season from Manchester United and is likely to sign permanently next summer.
He told the club's website: "When I'm on the pitch, I either win or I learn. I'll never consider myself a loser. Looking back, I've had a truly fantastic career.
"There have been many ups and downs, but that also means I've learned a lot. Playing for Barcelona, Ajax, Inter Milan, Manchester United, and now Trabzonspor in Cameroon is incredible."
Onana also recalled being nominated for Ballon d'Or goalkeeper award when with Inter Milan.
He said, "Then Alisson (of Liverpool) came to me: 'You've had a good season, but first let's see who wins, okay?' I told him I didn't care at all. I had already won. I wasn't there to win that award.
"My presence as the first black goalkeeper and the first African ever was already a great victory for me."