Cryptic Acrostic 3: Built So Fly

Question

This is an acrostic puzzle which uses cryptic clues. If you're unfamiliar with either or both of those, click the associated link.

A complete answer should give the quote, author and source, as well as solutions and explanations of the cryptic clues.

Oh, and in case you're too lazy to solve this with actual pencil and paper, I've created an interactive version that will autofill from the grid to the clues and vice versa. Have fun!

_{An accessible version for the visually impaired can be found here.}

Answer 1

The solved puzzle spells:

I was determined to master the first step of success: failure. For anyone who insists that taking one step forward and two steps backward will never get you anywhere, I protest: It will if you're walking backwards.; as shown by the first letters of the answers, this is a quote from George Watsky's How To Ruin Everything.

Clue explanations:

A. WINTER + GREEN
B. (-h)AWK + WARD<
C. TABLOID*
D. SWIFT (ddef)
E. _K + ISS
F. YOYO + MA
G. HALF-STAFF (punny def: "standard" is another word for a flag)
H. OSTRICH(-a)*
I. WEE + PING + WILL + O + W
J. TWEE + T(-r)Y (Tweety is a bird who pronounces /k/ as /t/, so in his catchphrase he says "tat" instead of "cat")
K. not sure - perhaps O(ATM + IL<)K, but it then seems like the inserted two parts are clued the wrong way around
L. ROTA(-no<)TED<
M. U + (a→(bo)P)WARDS ("top mark" = "first letter")
N. IN PAIRS*
O. N+E+W+S
P. ESSEN + C.E.
Q. V_ I_ + RUS
R. (th)EF(ts) + FORT
S. R_ + US + T_ B_ E_ + _L + T (&lit)
T. Y(E_)ARN
U. TAKE A SEAT*
V. HOP(-s) + SCOTCH
W. (I+O)+DINE (definition is "Periodically, I")
X. NERD(lihc)<
Y. G + RUN + _T