The decision taken by Leverkusen was right because Xabi Alonso's departure to Real Madrid needed a coach who could understand Leverkusen's overall style and although Ten Haq had not succeeded in handling Manchester United, he had a good record when he was a coach Ajax. The English League is slightly different from other leagues and that is why Ten Haq failed and did not fulfill expectations when he was a Manchester United coach because the competition there was quite competitive and a number of players he had were also not in good performance.
We need to realize this could be something that would make a lot sense if he does well. So, we could consider that this could be something that will move forward with it. Think about this, if we end up with ETH doing very well then he could stay here and even go back to being a manager for a bigger club again, if he does bad here too that means he is going to stay being bad manager and will just go down more and more.
This is why he has to show himself and he has to do better, there is no other option for him, he is going to do as best as he could. At United, he wasn't doing good, but before him, Ole didn't do good neither, and after him, Amorim didn't do good neither. So when you think of all of this, he could do better.