Let me first give you the tensile strength of both substances:
Diamond: 1600 MPa Steel : 2617 MPa
As you guys should know, tensile strength is how much a material can be stressed or pulled before it breaks. The data above shows that diamond is more brittle than steel. But, I thought a diamond is the strongest natural object in this planet. How can it be more brittle than something which is man-made? Don't the 4 strong covalent bonds in between the carbon atoms resist the pull and carry through huge amount of weight?