expert tier
Look at the pencil marks in the three highlighted cells. The first can only be 1 or 4. The second — which shares a row, column, or box with it — can only be 1 or 3. The third — which also shares one with the first — can only be 4 or 3.
Whichever the first cell turns out to be, one of the other two must be 3. So any cell that sees both of them can't be 3 either — including the marked cell, which still has another candidate left.