Let's assume we have exactly the same profile (rectangular or square or triangle or cylindrical etc.) beam under bending load. The reason I say exactly the same profile is because I would like both of the beam profile to have the same moment of inertia. The only difference between the beam profiles are one of them simply supported and the other one is fixed on both ends as shown below. If you apply the same force, which one bends more?

 Both Ends Fixed Beam


 One End Fixed Other End Simply Supported Beam



Both End Simply Supported Beam


Since both beams have the same E (module of elasticity) and I (Moment of Inertia) due to same beam profile, you can see that max deflection (△max) on a simply supported beam is 4 times bigger compared to both ends fixed beam.