Some monitors have tons of input lag (60-70ms) and that's the time it takes for you to see what you're typing to reach the display. This also includes the time it takes to see you move your mouse cursor too.
I did a huge write up on picking a good monitor for development which can be found at: https://nickjanetakis.com/blog/how-to-pick-a-good-monitor-fo...
I ended up buying the Dell UltraSharp U2515H http://amzn.to/2jF3WHp. It has very low input lag (10-15ms) and it runs natively at 2560x1440.