The most common and most likely answer to this crossword clue is the 4 plus 4 plus 6 letter word LICK ONES WOUNDS
I've seen this crossword clue in The Times
L
I
C
K
O
N
E
S
W
O
U
N
D
S
Buddy explains!
The straight part
We know that "retire to gain strength" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case retire to gain strength = lick ones wounds.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.