This is the 15627th most frequent Turkish word.
tecrübesinin
"His/her/its experience."
In this sentence, 'tecrübesinin' indicates possession ('his experience') and is in the genitive case due to the '-nin' suffix, showing relation to the subsequent clause about its importance.
Onun tecrübesinin çok önemli olduğunu düşünüyorum.
I think that his experience is very important.
Here, 'tecrübesinin' refers to the subject's ('your') experience and takes the genitive case ('-nin'), leading to the notion of necessity discussed.
Senin tecrübesinin gerekliliği konusunda haklıydın.
You were right about the necessity of your experience.
In this context, 'tecrübesinin' signifies the genitive case, denoting that the 'experience' belongs to the 'team leader', which is related to 'the effect' and the project's success.