The most common and most likely answer to this crossword clue is the 11 letter word APPOINTMENT
I've seen this crossword clue in The Daily Telegraph
A
P
P
O
I
N
T
M
E
N
T
Buddy explains!
The straight part
We know that "A candidate who fails to keep it is unlikely to get it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a candidate who fails to keep it is unlikely to get it = appointment.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
APPOINTMENT noun- The act of appointing a person to hold an office or to have a position of trust
- The state of being appointed to a service or office; an office to which one is appointed
- Stipulation; agreement; the act of fixing by mutual agreement.
- An arrangement between people to meet; an engagement.
- Decree; direction; established order or constitution.
- The exercise of the power of designating (under a power of appointment) a person to enjoy an estate or other specific property; also, the instrument by which the designation is made.
- The assignment of a person by an official to perform a duty, such as a presidential appointment of a judge to a court.
- (now in the plural) Equipment, furniture.
- A honorary part or exercise, as an oration, etc., at a public exhibition of a college.
- The allowance paid to a public officer.