Problem: How does the sentence end?

Jason always tries to improve every situation in his life unlike William because
Answer: William has a negative mindset.

Problem: How does the sentence end?

While in college, Jeffrey studied to be an engineer while Samuel wanted to be a musician because
Answer: Samuel was quite musically inclined.

Problem: How does the sentence end?

Most people feel that Brian is arrogant while Ian is quite humble because
Answer: Ian often admits that he makes mistakes.

Problem: How does the sentence end?

Jennifer was excited to play with Kayla but they had already left.
Answer:
Jennifer was regretful.