What a veneer is and what it solves
A veneer is a thin shell covering only the front surface of a tooth, rather like a false nail. It does not treat the tooth — it changes how it looks. That makes a veneer fundamentally different from a filling (which restores what is damaged) and from a crown (which covers the whole tooth and protects it).
And here is the part that often goes unmentioned: the tooth is ground down for a veneer. For a ceramic veneer, 0.3-0.7 mm of enamel is removed. Enamel does not grow back. So fitting a veneer once means doing it permanently: when it wears out a new one must go on, because the tooth can no longer be left without one.
That is not a bad thing — it just needs to be known before the decision, not after.