if there is a fine line between one thing and another, they are very similar although the second thing is bad.

There's a thin line between courage and foolishness. (often + between)

• the stage is set for something
• the state of play
• the status quo
• the story of life
• the story of someone's life
• the straight and narrow
• the straight and narrow path
• the straw that breaks the camel's back
• the swing of things
• the tables are turned.
• the tail end of
• the tail end of something
• the tail wagging the dog
• the thin end of the wedge
• the thing is
• the thinking man's crumpet
• the thinking woman's crumpet
• the third degree
• the three R's
• the tide turns
• the time is ripe
• the tip of the iceberg
• the toast of
• the toast of somewhere
• the tools of the trade