Components of the weapon system are the weakest link.
In my (somewhat limited) experience, I have seen the most problems by far caused by ammo, followed by magazines. I primarily shoot the Beretta 92 and weak ammo (reloads) has been the problem with nearly every malfunction I have had. The few others were caused by mags with weak springs (used mil surp).
The only malfunctions I have had with my glocks have been ammo related.
Just think of all the ammo problems with cheap .22 ammo!
Most of the malfunctions I've had with semi- autos have been caused by ammo especially in 22 lr.
Would being shot be considered a malfunction? If so than that adds to the things a person can do wrong. Are we talking about a self defense sanario or just any time your shooting?
For instance you've had some "Magazine" replies...... mags aren't a significant problem with glocks across the board, just like with many major platforms. However, with 1911s they can be a problem area as generally stock mags aren't GTG.