→ However, it was foolish to ask John to check your assignments. (Look) - This emphasizes the contrast between John's ability and the unnecessary action of asking him for help.

Jack stands a really good chance of being excluded from the team. (LEFT)
→ In all likelihood, Jack will be left out of the team. (This uses a more formal way to express the same idea)

Jack interrupted the moment I started the speech. (BROKE)
→ No sooner had I started the speech when Jack interrupted me. (This emphasizes the immediate nature of the interruption)

You must not surprise anyone with the plan.
→ It is important not to take anyone by surprise with the plan. (This rephrases the sentence to be more grammatically correct)

Jack's enthusiasm for the project was such that he ignored all the possible challenges. (ATTENTION)

→ Jack's enthusiasm blinded him to the potential problems of the project. (This uses a stronger verb to show the consequence of his enthusiasm)

Much to Jack's disappointment, the film wasn't as good as he had expected. (EXPECTATIONS)
→ The film fell short of Jack's expectations, much to his disappointment. (This rephrases while maintaining the meaning)

Contrary to everyone's expectations, John didn't succeed in passing the exam.
→ Everyone thought John would pass the exam, but he didn't. (This rephrases the sentence in a different way)

I would rather not have given in to the boss so soon.
→ I felt it was a mistake to surrender to the boss so quickly. (This uses "rather not" to express a preference for a different action)