The most common and most likely answer to this crossword clue is the 10 plus 4 letter word CAUTIONARY TALE
I've seen this crossword clue in The Guardian
C
A
U
T
I
O
N
A
R
Y
T
A
L
E
Buddy explains!
The straight part
We know that "Take warning from this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case take warning from this = cautionary tale.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.