Just what is "trigger pull" and why does it matter? It's a pretty broad question, but based on what I've experienced in terms of customers who brought guns they bought to me because the trigger is "too hard to pull", it's a question that needs some answers.
Trigger pull is the amount of energy necessary to pull a trigger through movement of the seer to release the hammer/striker to fire a projectile from a firearm, measured in pounds.
That's the easy part. The difficult thing to understand is that for some guns, trigger pull is fairly consistent, while for others it can be different depending on whether the gun is being fired as single action or double action. Some folks right now are thinking, "You had me, then you lost me." Yeah, yeah...I know. Now I have to explain Single Action and Double Action. These two terms refer primarily to pistols. If, when firing a pistol, you must first cock the hammer all the way back to the full cock position before you can pull the trigger, then you have a Single Action pistol. If your pistol's trigger mechanism, when pulled, lifts the hammer and releases it without having to first cock it, then you have a Double Action pistol. Some pistols are Single Action only, meaning they can only be fired after manually cocking the hammer. Some pistols are Double Action only, meaning that the hammer/striker can only be moved by pulling the trigger. Some pistols are capable of both Double and Single Action operation. Clear as mud?
Complaints I've received from customers who have had trigger pull with pistols they bought include:
"The trigger is too hard to pull back. After five rounds, l'm too tired to keep firing."
"I'm not strong enough to pull the trigger."
Single Action pistols tend to have a lighter trigger pull, which requires less strength to pull the trigger. Since the hammer is already cocked, the trigger finger only has to work against the trigger return spring.
Double Action Pistols tend to have a much stiffer trigger pull, requiring more strength to pull the trigger. In addition to the trigger return spring, the trigger finger also must overcome the tension of the much larger master spring which propels the hammer toward the firing pin.
So what does all this mean? It means there are more things to consider when purchasing a firearm than just how big the bullet is. For some people, trigger pull is a big deal because of hand strength/size, joint health, and/or age. For these reasons when considering a firearm for purchase, I recommend firing a full box of ammo from the kind of pistol you are interested in at a well designed and safely operated range. Some ranges (like Red's in Austin) have guns for lease that you can rent and fire, which will give you a good idea for the trigger pull required to fire the gun.
If your hands are small, or if you know your hands aren't terribly strong, then ask about Single Action, or Double/Single Action. You'll want to make sure you can both pull back the hammer AND pull the trigger without difficulty.
If you've already bought a pistol, only to realize later that the trigger is too hard to pull, then there are some things a gunsmith can do to help to adjust the gun's spring tension to somewhat ease the burden of pulling the trigger, but it's always better to fit a shooter to a gun than to retrofit a gun to a shooter.