Many modern handguns do not have a manually activated safety. The Sig M17/M18 does, but the safety only blocks the trigger from moving rearward far enough to fire.

It may not block the trigger from moving enough to disengage an internal, automatic safety that prevents the firing pin from traveling all the way forward if it is released due to a malfunction. It is also possible that the firing pin block safety does not always work even if the trigger is fully forward.

consumer versions of this pistol do not have a manual safety

they have internal safety mechanisms to prevent discharge, and these are important if you carry with a round chambered - in a striker-fired pistol, the firing pin is under tension and is only being restrained by the trigger and internal safeties

this is why I do not carry with a round chambered, if you appendix carry and something goes wrong, you will be missing an important appendage

This is why I carry a gun I trust. I keep one chambered at all times, pointing at my junk. I am not concerned about my junk. I am much more concerned about not being able to get a shot off in time if I ever need to use it.

Common failures would be to use the wrong holster, defective holster, or get some object in the holster that could snag the trigger as you put it in.

Some guns, striker fired, do not have safeties as you may think of them.