Introduction:
Taro ran in the direction of the stream because he was motivated by the possibility of receiving a reward. The specific details of the reward are not mentioned in the question, so we will explore possible reasons why Taro would run towards the stream.

Possible Reasons:

1. The reward was related to the stream:
It is possible that the reward Taro was promised had something to do with the stream. Perhaps there was a valuable item or treasure hidden near the stream, and Taro was eager to find it. Running towards the stream would increase his chances of discovering the reward.

2. The stream provided a clue or hint:
Another possibility is that Taro received a clue or hint that led him to believe the reward was located near the stream. This clue may have mentioned the presence of a stream or described a location that was identifiable by its proximity to the stream. Taro's decision to run in the direction of the stream could have been driven by his desire to follow the clue and ultimately find the reward.

3. The stream represented a milestone or checkpoint:
In some situations, a stream can serve as a milestone or checkpoint along a journey or task. Taro may have been instructed to reach the stream as part of a larger challenge or quest. By running towards the stream, he may have been trying to complete an important step towards achieving the reward.

4. The stream was a known meeting point:
It is also possible that the stream was a prearranged meeting point where Taro was supposed to meet the person or group offering the reward. By running towards the stream, Taro would be able to reach the designated location quickly and efficiently. This would allow him to receive further instructions or claim his reward.

Conclusion:
Without specific details regarding the reward, it is challenging to determine the exact reason why Taro ran in the direction of the stream. However, the possibilities mentioned above provide some potential explanations for his actions. The specific context and circumstances surrounding the reward would ultimately determine the rationale behind Taro's decision to run towards the stream.

Taro run in the direction of the stream because earlier he had
never heard or seen a rushing stream in the forest also he was
thirsty.