there can only be one possibility for a triangle when given the lengths of all the sides but for a quadrilateral the measure of the angles could differ depending on the person building the,. this is because triangles are more stable than quadrilaterals meaning that their side lengths follow a lot more rules than quadrilaterals do, for example the length of the side lengths can indicate whether or not that triangle is an acute, obtuse, or right triangle, and this is also evident by considering that you can use the SSS theorem to indicate two triangles are congruent, but for quadrilaterals you cant do that
