The most common and most likely answer to this crossword clue is the 15 letter word UNDERPERFORMING
U
N
D
E
R
P
E
R
F
O
R
M
I
N
G
Buddy explains!
The straight part
We know that "Being relatively unsuccessful" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case being relatively unsuccessful = underperforming.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.
What does UNDERPERFORMING mean?
UNDERPERFORMING verb- To underachieve, to not reach standards or expectations, especially with respect to a financial investment.
- That performs less well than required