The first thing to say sounds quite harsh, but it is true - if the possibility of losing your craft is more than you can bear, then flying an expensive UAV is not for you. Every time any one of us puts a craft in the sky, we all know there is some (fairly minimal) chance that things will go wrong, and in worst case scenarios we can lose our flyers or have to watch them smash themselves into pieces as they hit the ground. That feeling will never not be horrible, unless you only fly cheap little race quads for whom crashing is fully expected every time and repairs can be done cheaply at home...
As you know, photo drones like this are expensive, but still a long way short of flawless, and there is always the risk that some component may fail in flight. It is our job as responsible pilots to minimize these risks, by preparing properly, undertaking diligent maintenance checks every time we fly, taking our time before launch, flying sensibly, and by not flying anywhere or in such a way that other people or property can be damaged by our machine, should it fall !
The reasons that UAVs can fall from the sky are manifold and varied - sometimes it's pilot error, pushing batteries way past the warnings, sometimes a battery that has been inserted carelessly can come loose in flight, or sometimes, some part of the electronics can just fail, which may have the same result. If any motor fails on a quadcopter, for example, it will fall from the sky. I like the additional motors on a hexacopter like my TH for that reason, which can at least remain in (landable) flight with a motor down. But it does have to be said, motors failing is a relatively rare event without external influence (usually collision or bird strike). Usually falls-from-sky are power-related in some way.
My advice is as follows:
1. Accept that crashes do happen, even to the best of us...
2. Make sure you are doing everything you can to avoid them happening to you.
3. Make sure you are as informed and knowledgeable as you possibly can be about your particular model.
The latter part of that involves an incredible amount of reading - you should read all the forum posts you can find about your flyer, and be as familiar as you can with the sort of problems its users encounter, as this gives you maximum awareness of things you need to watch out for. But also try and retain perspective, and remember that for every post you read about a Q500 horribly crashing, there are most likely 100 flight sessions that didn't need forum posts because everything was fine...
UAV flying is a scary thing to do initially (I didn't even stop physically shaking while my craft was airborne until about my 20th flight !) but time and experience (and successful flight sessions) will begin to build your confidence in your craft and your own safety checks, and eventually you should find that you are enjoying it more than you are scared of things going wrong !
Happy, safe flyings !