This is a complicated question that really deserves a longer answer than here in the FAQ's- see our article on cracking. The bottom line however is- yes. Concrete is a rock-like substance that expands and contracts with temperature changes, as well as other factors having to do with the chemical process of the actual "drying" (which is in fact an exothermic chemical reaction) of the concrete. Control joiints must be put in, whether they are hand tool joints, or sawcuts, in a timely manner to convince the concrete to crack in the joints created for them. Failure of a slab however is another thing. While a hairline crack might develop for some unknown reason, the actual concrete slab failing is usually due to either a poor design/installation with the sub-grade often being poorly compacted and/or wet. Other factors are the use of excessive water in the concrete leading to uncontrolled cracking, crazing, and slab failure. Pouiring concrete on mud/muck can lead to sub-grade failure, with the dirt shrinking, leaving a void below that especially with car traffic on a driveway, that can lead to slab failure.