A good foundation does more than just not letting your home to sink into the ground. Additionally, it keeps out the moisture, insulates from the cold, and resists movement of the earth round it.
A quality foundation requires a lot more than simply digging a hole and pouring some concrete into molds.
It must be tailored to make it perfect fit for your future home, taking into consideration soil conditions, water tables, even the quality of the back-fill.
And as with a custom project, every detail must be ideally chosen: the base properly compacted, the form-work set up right, the concrete free of voids. Neglect even one of them, and the most carefully poured foundation can fail.