You can see the people failing in this regard all time, even with a simple glance at their body.

People (males especially) often focus on the muscles they can see (chest day bro!).

This is the typical postural irregularity seen in those who practice poor exercise programming in regard to strength training. The over developed pectoral muscles of the chest shorten, causing the shoulders to internally rotate, while the underdevelopment muscles of the upper back and posterior shoulder become slack in comparison. The extensor muscles of the neck elongate to compensate for the fault occurring below them.

To add insult to injury, this is precisely the position that lots of us sit in for 8+ hours a day. So many folks are sitting in this position all day, then going to the gym and strengthening the dysfunction even further!

The devil is in the details and programming to a professional standard is key. A simple rule of thumb is to pull twice as much as you push. Get that chest opened out and shoulders externally rotating.