Could you please check this sentence, especially red parts? You can change the sentence in a more concise one if you want. Thanks.

At the end of the day, every group found that focusing on its/their own need would not promise its/their success; win-win situation should be dominant.
Hi Davoodl, and welcome to English Forums.

Do you consider each group acting as a unit? If so, use "it." Do you consider each group acting as a collective group of individuals? If so, use "their."

However, "At the end of the day," is a bit trite, unless you literally mean that they spent one day doing this.

Eventually, the groups all discovered that if they focused only on their own needs, success was not guaranteed, but when they working for win-win solutions, every group prospered.

Try something like that.
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Ultimately, each group found that focusing on its particular needs did not ensure success. Therefore, choosing a win-win situation should be the dominant approach.
Thanks, friends.
I exactly mean that at the end of the day something happened and the second day was started in a different way.
I like both sentences, and I see the difference between a native english person and non-native Emotion: sad
HI Davoodl,

I'd suggest saying "At the conclusion of the first day," because "at the end of the day" is an over-used expression that means "eventually," and readers may not at first realize that you meant it literally.

Don't be discouraged. A lot of native speakers have trouble constructing good sentences too! Yours will read more and more fluently the more you write.
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