As brass gets reloaded several times, it gets less malleable and often dies need to be turned in a little. Cases shot in a different rifle may also require more sizing.
I once bought a set of 6mm Rem dies from a reputable manufacturer that were actually warped at the factory during heat-treating. Loaded rounds rolled across a table resulted in bullet noses going around in a circle. Rounds didn't chamber. The die was returned and the new one was fine, but now I always roll my first reloads from a new die set.
People are like rifles. Some are tried and true, having great eyes, personality, and fun to be with. Others never seem to hit the mark with you. Still others go off half-cocked. Still, it's nice to know most of them.