And an ever tougher scrap for success with Mercedes next year.
Talking to reporters ahead of this weekend's season-closing race, the Finn said he feels he has to prove himself again to secure a long-term deal with the 'silver arrows.'
"The season has been tough," he said.
"There have been many races where Ferrari had the upper hand and even lately Red Bull has been really strong so it has definitely not been like the last three years.
"It has been tough and it is only going to get tougher. I have unfortunately had only two wins this year.
"I was definitely hoping for more like I said, but I am glad I have proven myself and the team signed me up again for next year.
"Next year's going to be the same thing. I need to again prove if I am going to stay with the team for a long time."