A Hidden Single flips the question around. Instead of asking “what can go in this square?”, ask “where can the 5 go in this box?”. Each row, column and box needs every number exactly once. If a number can only fit in one square of a unit, it must go there, even if that square has other candidates too.
This is the technique behind most quick solves. Pick a number that already appears several times on the grid, then look at each box that is still missing it. Lines coming from the 5s already placed rule out squares, and often only one square survives.