Sentence examples for the thing from inspiring English sources

'the thing' can be used in written English, however, the context in which it is used matters when determining whether or not it is grammatically correct.
Depending on the context, the phrase could be used as a noun, or it could be used as a pronoun. For example: "I'm not sure what to do, but I know the thing I should do is talk to him." (noun) "The thing is, I don't think I can make it to the meeting." (pronoun).