The law of transitivity of identity is that if a bears resemblance to b and b bears resemblance to c, then a bears some resemblance to c. in this case, to follow through with the law would be to say that a, Yoeli will get the job, b, Yoeli has ten coins in his pocket and c, the person who will get the job has ten coins in his pocket. these three ideas are interdependent. the belief that Yoeli will a, get the job and b, has the ten coins in his pocket results in the transitive conclusion that the person who will get the job has ten coins in his pocket. in the afformentioned example, the justified true belief in question is that the person who will eventually get the job. the law of transitivity is what gives chaim the justifiability to conclude as such. he has assumed, apparently justifiably, that yoeli will get the job and that yoeli has ten coins in his pocket. armed with these two pieces of information, he can justifiably assume that the person who will eventually get the job has ten coins in his pocket. it is this belief which is under discussion. we can call this belief “p.” In the original laws for defining knowledge, we need three things, for p to be true, for chaim to believe that p is true and for him to be justified in doing so. in our case, p is eventually true because even know it was based on false assumptions, namely that Yoeli would get the job, it was true. the person who got the job had ten coins in his pocket. the other two conditions are also met, he was justified (by the law of transitivity of identity in believing b to be true and the final condition, he believed b to be true. therefore, gettier is justified in asking his question.
this is an idea which is difficult to convey in writing but bear with me while i try one more time to talk it all the way through. Gettier poses that the three conditions of knowledge, ie, believing p to be true, being justified in believing its true and it eventually being true, are insufficient as a definition of knowledge. to illustrate this insufficiency, he poses the example in the OP. In this example, P, is the belief. (That the person who will get the job has ten coins in his pocket.) Chaim believes it to be true. condition one met.
Chaim is justified in believing it to be true. (as he has employed the law of transivity of identity and since he believes Yoeli will get the job and that Yoeli has ten coins in his pocket, he is justified in believing that the winner will have ten coins in his pocket.) Condition two met.
P is true. The winner (albeit not the person chaim originally thought would win) has ten coins in his pocket. Condition three met.
And this is exactly the point of Gettiers question. It is true that all of the three conditions were met, but yet by virtue of the fact the the justification, although justifiable at the time of thinking it, was false and so with this flaw in Chaims thinking, how can we still consider that he KNEW that P would be true. The fact is that his thought process was flawed and the outcome cannot vindicate his original thought because it was flawed. As such he concludes that there must be a revised definition of knowledge and Chaims belief in P cannot be considered KNOWLEDGE of P.
On a side note, an original prediction coming true cannot be used to support the original thinking of it. If i flip a coin and say i know it will land on heads, everyone will agree that i have a 50 percent chance of getting it right, and so the fact that it eventually happened cannot have any bearing on the original statement of knowledge. The original definition of knowledge doesnt rely only on the outcome, it uses it in a combination of three conditions, but as explained above, it cant even be used as one of three. The fact that is was true has to be an irrelevant fact.
Please feel free to ask any questions if you feel like my answer lacked sufficient explanation.
Good luck 😉