If two polygons have different sets of side lengths, they can’t be congruent.

For example, the figure on the left has side lengths 3, 2, 1, 1, 2, 1. The figure on the right has side lengths 3, 3, 1, 2, 2, 1. There is no way to make a correspondence between them where all corresponding sides have the same length.

If two polygons have the same side lengths, but not in the same order, the polygons can’t be congruent.

For example, rectangle $ABCD$ can’t be congruent to quadrilateral $EFGH$. Even though they both have two sides of length 3 and two sides of length 5, they don’t correspond in the same order.

Two figures, A B C D and E F G H. Figure A B C D is a rectangle with side length 3 and base and top length 5. Figure E F G H has base length 5, top length is 3, left side length is 3 and right side length is 5.

If two polygons have the same side lengths, in the same order, but different corresponding angles, the polygons can’t be congruent.

For example, parallelogram $JKLM$ can’t be congruent to rectangle $ABCD$. Even though they have the same side lengths in the same order, the angles are different. All angles in $ABCD$ are right angles. In $JKLM$, angles $J$ and $L$ are less than 90 degrees and angles $K$ and $M$ are more than 90 degrees.