Well...I would say...do not despair. Sounds like this is just a matter of defective lights, not your competency or ability to understand - not at all.
I'm not an Olight user and haven't ever tried to keep up with their offerings' characteristics other than (stupid) proprietary battery designs. It's good that they took care of you, twice even, so you're not out any cash, just a little time and frustration. You might search this forum and CPF a little, maybe even youtube, to see if that particular light and time of manufacture is known to have some defects. Sometimes those appear right away and sometimes they just fail over time. If the third one dies, you might ask them if they're willing to replace it with a similar model if the design is likely to fail yet again (assuming there was a design issue and they addressed it...that happens a lot with many manufacturers if they keep the model for sale over time).
Hard to say anything about your light's issue but of course generally flickering indicates an unsteady connection of the electricity somewhere. Very often that can be something as simple as stray grease/oil on threads or battery contacts and cleaning it up fixes everything. Many lights use the connection between tail cap and tube body as a conductor, so having those surfaces clean is smart, too (and the same on the head end). Many lights also use little skinny threaded rings to clamp the driver board into its place and/or the tail spring board into its place. With normal use sometimes those retaining rings will loosen up a little and need to be snugged down again, or perhaps they were never snugged properly at the factory. When they get loose the electrical connection either cuts out or becomes erratic and weird things can happen. So checking these basic things is something easy that you can do and watch out for.
Defective batteries are rare so as long as you're using quality ones you shouldn't see issues there (contacts clean of course). And then that brings us to the nitty gritty of more complex failures, which does take some learning and basic tools to try and diagnose. Drivers seem to fail a lot although some last many many years with constant use and never give any issues at all. But if a solder joint somewhere was poor to begin with, it may fail down the road and cause who-knows-what kind of issues, and sometimes the little chips and components can fail, too. Maybe the stripped end of a wire wasn't done properly or positioned correctly and works for awhile before causing a short in a circuit. These are things that are harder to figure out and understand, but if you want to (or need to) you certainly can. And this forum is fantastic for that.
Other than the basic cleanliness and snug connection stuff, none of this is competency...it's just living with affordable electronic designs. :) When we pay more money, sometimes the designs and parts aren't necessarily any better than less expensive items, but you're often paying for some availability of service after the sale, parts, warranty replacement, etc (and of course....the dreaded Marketing). With some companies you're kind of on your own to figure it out and fix it, but ones like Olight and some others will be there for you. They may not be "budget" pricing but they do have that going for them. And then there are some companies who charge more, promise the service and assistance, and still leave you out in the cold.