It looks like Flash has been betrayed by his very own sidekick. A clever attack by Kid Flash accidentally revealed an obvious, yet extremely effective Achilles' heel for the Fastest Man Alive.
Every superhero generally has a critical weakness that diminishes their powers or slows them down enough for a villain to do some serious damage. Superman, of course, has the radioactive slivers of his home planet known as kryptonite while Green Lantern couldn't fight back against the color yellow for decades. Even the Flash, for all his amazing speed, hasn't been impervious to a few weaknesses over the years. The Rogue Captain Cold arguably has the most famous deterrent against the Scarlet Speedster in the form of a 'cold gun' that completely stops atoms in their place. While the Flash has been able to mostly work around Cold's infamous weapon, it shows that there are flaws Flash can't easily outrun. Case in point, the Flash's own sidekick revealed that the hero has one of the most obvious weak points that's been completely overlooked
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In The Flash #21 by Francis Manapul and Brian Buccellato, Barry Allen tracks down a killer going after people who have a connection to the Flash's Speed Force. After discovering a young hero has taken up his symbol, Barry seeks out the Teen Titan calling himself "Kid Flash" to see how he fits into the equation. Kid Flash, however, doesn't feel like talking and leads Barry on a chase around the world. Despite his best efforts, the Titan realizes he's no match for the elder Flash. In a desert, Kid Flash whips up a minor dust storm to rob the Flash of his sight so the junior speedster can finally give Barry the slip.
While there's a chance that the sidekick could one day be faster than Barry Allen, Kid Flash was definitely outmatched by someone who had super-speed for a good five years more than him. But the Titan's quick thinking revealed that despite all Barry's experience as the premier speedster of the DCU, he hadn't accounted for the need to protect his vision. Kid Flash's attack might have been a bit underhanded, but he exposed an interesting vulnerability.
Granted, impaired vision isn't on the same level as red suns or magic, but it's clearly effective at distracting the Flash. After all, if Barry can't see what's in front of him, what's the use of super-speed? There are plenty of Flash villains that could easily exploit this weakness. Mirror Master could direct sunlight into Barry's eyes, or Abra Kadabra could conjure up a trick to put Flash in complete darkness. With a bit of creativity, there's no limit to how a Rogue or any other villain could temporarily impede Flash's sight in order to gain an edge when fighting him. While it's not the worst weakness in the world, Barry's old sidekick made a pretty good argument for Flash to add some goggles to his costume at the very least.