Do you mean that you add a row for the next day based on existing rows. Then the statement could be something like:
insert into Thoughts (TheThought, DisplayDate)
SELECT 'Some thought', COALESCE(MAX(DATEADD(Day, 1, Display)) , GETDATE())FROM Thoughts
However there are several other ways to resolve the date problem without fixing it into the database. For example selecting Nth row based on some date could also be a usable solution.