How to describe a person who has done well in every task except one, but he has done extremely bad in that 'one' task

Question

I mean, "How to describe a person who has done well in every task except one, but he has done extremely bad in that 'one' task which adversely affects the overall result. I don't literally mean one though.

For example, someone gets extremely good marks in every subject (except one) in school -- he's the top scorer in each individual subject (except one) -- but he's got extremely low marks in one of them, and as a result he's no more first.
We can say he is inconsistent. But it's not exactly what the condition is. It doesn't emphasize the extremeness. Bottleneck is another word which I think could be used. But how do we say it -- "He made a bottleneck?"

I'd prefer the word/phrase which fills the following blank:
"He is ____."

Answer 1

He has an Achilles heel. This implies that his excellence is crippled by a single, titanic flaw.

Apologies for the wiki-link, but the OED didn't capture the full meaning. Link-Wiki

Answer 2

You could say He has a tragic flaw

A flaw in the character of the protagonist of a tragedy that brings the protagonist to ruin or sorrow.

American Heritage Dicitonary

A more technical (and classical) term is hamartia. Oxford Dictionaries Online

Similarly, the term fatal flaw is also used. Wikipedia

Answer 3

One might say he has "a blind spot", which in this sense is defined by Merriam-Webster as " an area in which one fails to exercise judgment or discrimination".

Answer 4

He is just short of perfect?

Or something like... "a blemish on an otherwise perfect record."

Answer 5

Depending on details of the context, you might say this person has feet of clay.

From Cambridge Advanced Learners Dictionary & Thesaurus:

have feet of clay

to have a ​bad ​quality that you ​keep ​hidden: Some of the ​greatest ​geniuses in ​history had ​feet of ​clay.

Often the "feet of clay" refer to a hidden character flaw, but they can refer to any other shortcoming that is unexpected. Compare the definition from Dictionary.com:

feet of clay

noun

1. a weakness or hidden flaw in the character of a greatly admired or respected person: He was disillusioned to find that even Lincoln had feet of clay.

2. any unexpected or critical fault.

Note, however, that all these definitions imply that the weakness was somehow hidden or unexpected. So if it was known from the very beginning that a person was a virtuoso in all subjects at school but one, and that he or she was bound to fail in that one subject, "feet of clay" may not be the most apt expression. If the idea is that most people think this person a very good student, and that the poor performance in one subject is somehow surprising or difficult to reconcile with the student's other abilities, "feet of clay" might be a suitable description.

One other connotation of the phrase is that this one weakness in the person will lead to their ultimate downfall in some way (similar to an Achille's heel). This particular connotation does fit the case of a student who would have been first in his or her class if not for one subject. From The Free Dictionary:

feet of clay

A flaw or vulnerability of someone who is otherwise admirable. In the Bible's Book of Daniel, King Nebuchadnezzar dreamed that he saw a statue made of gold, silver, and brass, but with feet of clay. Daniel interpreted the vision to mean that the clay symbolized the Babylonian Empire's vulnerability and imminent collapse. (See Achilles' heel.)

Answer 6

As suggested by Dan the comments to another answer, you could say he is Napoleonic^[1]. However, there are a lot of ways one could resemble Napoleon, so it would be better to stretch your one-word criteria a bit and say:

He met his Waterloo^[2].

_{Suggested by Doug Warren and refined by RemarkLima in other comments on the answer linked above.}

This indicates a pattern of success that was ended due to one "battle", and the metaphor is readily apparent to anyone who understands the reference. (Napoleon won around 60 battles prior to Waterloo and while he lost around 6 others they were not so final.)

Answer 7

To say that he isn't suited to the full set of tasks required.

He is incomplete.

To say that he fails at a critical moment.

He is a choke artist.

Answer 8

For a person who is obviously talented and gifted at what they do, but performs poorly on the last or final task you could say:

1. He failed to deliver the goods on the given day

The Free Dictionary defines the idiom as

deliver the goods
if someone or something delivers the goods, they do what people hope they will do

• So far the team's new player has failed to deliver the goods. He hasn't scored in his first five games.

I would be more charitable and suggest that the person simply had a bad day (at the office).

2. Lewis Hamilton blames 'bad day at the office' after finishing sixth in Hungary
   _{source: Sky Sports}

Answer 9

"He is exceptional but fallible."

'Fallible' can indicate that there exists a weak area or areas, and is generally used in a context were the subject is otherwise extraordinary. If you want to underscore past history in failing:

"He is exceptional but demonstrably fallible."

(Or 'historically' or some other word modifying 'fallible' to indicate past experiences leading to that conclusion.)