Copying a key looks like a commodity purchase. However, the copy is only as good as the key it was cut from, and that single fact explains most of the complaints people have.
Copies inherit wear
Your key has worn since it was cut, so a copy taken from it inherits that wear. Consequently a copy of a copy drifts further, until eventually it will not turn. Therefore a locksmith decoding the lock and cutting to the original code produces a better key than any duplicator can.
Blank quality matters
Cheap aftermarket blanks use softer brass, so they wear faster and snap sooner. Consequently a key that costs a dollar less may last a third as long. Moreover a soft key in a hard cylinder does the wearing, which means you pay twice.
Restricted keys cannot be copied
If your key is stamped do not duplicate or has an unusual profile, it may be a restricted keyway. Consequently no kiosk can cut it, by design. Therefore copies require authorisation against a documented list, which is the whole point of the system.
How many spares to keep
Two per household member plus one with a neighbour covers almost everything. Additionally, keep one unused as a reference so future copies start from an unworn original. Above all, do not hide a spare under the mat, because that is the first place anyone looks.
Questions we get about this
Why does my copied key not work?
Probably cut from a worn key. Consequently cutting to the lock is better.
Can you copy any key?
Most. However, restricted keyways require authorisation by design.
Are cheap blanks worse?
Yes. Softer brass wears faster and snaps sooner.
Where should I hide a spare?
Not under the mat. Give it to a neighbour or use a decent key safe.
