Natural nails are like skin, in that they sweat oils/moisture (so to speak). Some people have naturally ''oily'' or moist nails, some naturally dry. Just think if you applied nail polish to your skin, how long would it last before wearing off? The tips show the quickest wear due to the fact that we use our nails as tools. (typing, digging in our purse, picking up items off the floor, scratching off sticky labels)
Tips to longer lasting polish:
Start with spanking clean, dry nails. Any residue, soap/oil etc will result in chipping, flaking off fairly quickly. ALWAYS use a good base coat. Apply 2 thin coats of polish and then a coat of top coat. The trick is not to slather on the layers heavy. Thicker is not better. Thickly applied polish will not dry consistently and will just peel off.
hope that helps....