You can make four strips of wood, say 1" wide by 1/8" thick.   Take a pair and tape the middle together, take another pair and only tape the ends.   Feel the difference in stiffness...

The one you one tape in the middle will act as two separate beams.  The one you taped at the ends will act as one beam with double the thickness.  How much stiffer will the beam that is taped at the ends be?   Since deflection is proportional to moment of inertia, and I is proportional to thickness cubed, it will be 4 times more stiff!  Two cubed is eight, and 1 cubed times 2 members is 2, and 8/2 = 4.  It will be double the strength and 4 times the stiffness - just by taping the ends so it resists horizontal shear and acts as a composite beam.  Go ahead and try this simple experiment.