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Is this game just luck based?

So in a season i tried a strategy and i won with another guy being 30 seconds behind me. 1 season later we both used the same strategy as before but he won with a gap of 20 seconds. the only difference this time is that it was 2°C lower than the season before.
Could someone explain why this happened?

It was at Bahrain: i did a S/H/H and he did a M/M/S. first season it was 29°C, second season it was 27°C.

Push levels, KERS & DRS use, stint lengths & fuel, car design, drivers, tyre temps & tyre wear management, many factors.

You said he used the same strat as you when he won, meaning he did S/H/H as well? Bahrain is usually hot so Hards run really well there.

Well no, in the second season he used M/M/S just like in the first season. i used S/H/H for both seasons.

Looking at the race results for Bahrain, he got the overcut on you, but for some reason you were slower on Hards in the last stint. Were your tyres overheated? And what's the car design difference.

Drivers aren't identical either...