A glass should be held firmly in between fingers or else, the chance of drop will increase. The rule is engraved in our brain. Holding it firmly is the normal instinct. We are aware that falling will cause breakage and spillage of contents. Sometimes, falling cannot be prevented, the glass breaks and the contents are wasted.
1) Hand injury. The hand is wounded or suffering from arthritis. Holding it firmly is hard when the hand is in pain.
2) Too young or too old. Toddlers find it hard to hold a glass or any other object firmly. The thing might be too heavy or the hands are not strong enough. The same principle applies to old generations.
3) Holding it with slippery hands – soapy or oily. Drop incident is very likely.
4) Someone in a hurry causes breakage of kitchenwares such as plates and glass. This is often the cause.
This glass is slip proof. The brim is protruding sidewards. It was designed to cling to fingers in case of accidental slippage.
KFC Fast Food Restaurant is using this kind of glass. It is not only slip proof, it is also break resistant. It is a plastic glass.
Most of the disposable drinking cups have this design. Made of soft plastic material so holding it firmly is not possible. The protruding brim prevents the accidental drop.