With the design of the M14. And that was to put a full auto switch on it. By doing that, they tried to make it something it never should have been, which is why 90% of them had the switch removed and the "selector lock" installed, making it semi only. If they hadn't fooled with the full auto in the first place, it would have been hailed as a great rifle and a worthy replacement for the M1.
I doubt it M14 would have ever been successful regardless of it's mode of fire. Yes, the full-auto capability hastened its demise but regardless the big bore battle rifle was on its way out in favor of the new "assault rifle" as the standard issue infantry weapon. What armies wanted was a light weight, pistol gripped, mid-powered, high capacity, select fire rifle. The Germans set the trend in WWII and Russia capitalized on it right away. The US and our allies lagged behind for years but ultimately we realized we had to make the switch.
The M14 offered very little advantage over the M1 Garand. About it's only improvement was the addition of a 20 round magazine and slightly shortened overall length. The Army really hoped that the M14 would be an answer to the AK47 and it wasn't. It was a failed design right out of the gate for its intended mission. But that's not to say the rifle is a bad design, because it's not. It's a very good design.
Today the M14 serves in a much better role in our armed forced. As a designated marksman rifle, it adds range and power to a squad. It also serves quite well in special units that need weapons with diverse capabilities depending on their mission.