Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:
Identify the mistakes in the given sentence and explain why it is wrong

### Input:
The man had bought a horse but the horse wasn't good

### Response:
The sentence is grammatically incorrect. The correct sentence should be "The man had bought a horse, but the horse was not good". The mistake is the use of "wasn't" instead of "was not". This is incorrect because "wasn't" is the incorrect form of "was not".