If you need, or want, your light to work all the time no matter what, buy a Surefire, HDS, Streamlight, or similar. They are as reliable as a light can be, and if you ever do have a problem they will make it right without hassling you. I've had Surefire parts break, and they don't even require you to send the light in - they just send you the part on your word.
The top tier Chinese lights (Eagletac, Fenix, Olight, etc.) can be good, until they aren't. They seem to be in a neverending 'lumens war' and worry more about who can print the biggest numbers instead of designing consistent lights that don't overheat or have other problems. As far as reliablility, there are lots of reports from people who had a light that worked great until they dropped it or got it wet then learned that a warranty isn't much good if it costs you an arm and a leg to ship the light to wherever to get it fixed.