“They don’t get big by being dumb/stupid” is a hunting and fishing adage, meaning that a big animal/fish has some survival smarts. “There are some big (deer) over here but they’re not the dumb ones. They don’t get big by being dumb” was cited in 1968. “Big bucks don’t get big by being stupid” was cited in 1981.
 
“‘They don’t get big by being dumb,’ Hubbard said, playing the fish” was cited in 1981. “Fish don’t get big by being dumb” was cited in 1990.
 
   
15 December 1968, Rockford (IL) Morning Star, “Outdoors” by Bill Vint, pg. E5, col. 5:
“There are some big (deer) over here but they’re not the dumb ones. They don’t get big by being dumb.”
(Ed Freeman, a conservation officer.—ed)
 
Google News Archive
17 March 1981, St. Petersburg (FL) Times, “Mets’ star Kingman finds some strikes he likes on Tampa Bay” by Jeff Klinkenberg, pg. 9C, col. 2:
“They don’t get big by being dumb,” Hubbard said, playing the fish.
 
16 December 1981, Port Arthur (TX) News:
Big bucks don’t get big by being stupid.
   
Google Books
Hunting Superbucks:
How to Find and Hunt Today’s Trophy Whitetail and Mule Deer
By Kathy Etling
New York, NY: Outdoor Life Books
1989
Pg. 221:
They don’t get big by being stupid, even where we can offer them a measure of security.
   
Google Books
New York Sportsman
Volumes 19-20
1990
Pg. 80:
Fish don’t get big by being dumb.
 
Google News Archive
1 December 1994, Kingman (AZ) Daily Miner, “Windy weather doesn’t bother stripers” by Chet Moreland, Weekender, pg. 9, col. 2:
Remember fish don’t get big by being dumb.
 
Google Books
Off-The-Wall:
A Graduate Course in Deer Hunting
By Jack Van Riper
Durand, MI: Chippewa Adventures
1995
Pg. 67:
Record book bucks don’t get big by being stupid.
 
Google Books
Backcountry Fly Fishing in Salt Water
By Doug Swisher and Carl Richard
New York, NY: The Lyons Press
1995
Pg. 130:
These fish don’t get big by being stupid.
 
Google Groups: rec.outdoors.fishing.bass
Confused…
Chris Rennert
8/18/03
Fishing Nut,
There could be a lot of factors involved, including area and presentation.
You always hear fish don’t get big by being stupid.
     
Google Books
Fishing Alabama:
An Angler’s Guide to 50 of the State’s Prime Fishing Spots
By Ed Mashburn
Guilford, CT: The Globe Pequot Press
2009
Pg. 129:
Keep in mind that there are some very big fish in Lay Lake, and they don’t get big by being dumb.
 
Twitter
Sassy Does
‏@SassyDoes
We all have probably heard the saying “Big bucks don’t get big by being dumb”! Click “LIKE” if SCOUTING has been… http://fb.me/2c6qpAtRD
2:02 PM - 27 Jul 2012
 
Sun Sentinel (Fort Lauderdale, FL)
‘Addictive Fishing’ host Blair Wiggins is ‘the real deal’
Up close and personal with the popular fishing personality
June 27, 2013|By Steve Waters, Sun Sentinel
(...)
His favorite fish to catch: “Trout over 12 pounds,” said Wiggins, whose personal best was a 141/2-pounder that he caught in Cocoa Beach. “I love big trout, just because they’re so smart and wise and old. They don’t get big by being dumb.”
 
Florida Sportsman
Cobia and the Rays
by Brenton Roberts • June 24, 2015
(...)
This cobia surely validated the old saying, “They don’t get big by being dumb.”