that's the thing

1.
USUKGeneral Englishneutralinformalspoken
- Used to identify or single out the specific item, factor, or matter being referred to.
- Used to introduce the central point, reason, or problem in a discussion.
2.
USUKGeneral Englishinformalcolloquial
- Used to endorse or recommend a particular action as appropriate or desirable (equivalent to 'that is the thing to do').
- Used to express appreciation for a particular quality or characteristic of someone or something ('that is what I like about X').

Examples: