For me, the best way for me to ensure that I have a safe way down is that I attach my rappel line on the ground, & use it as a tether on the way up, & at height. I've been practicing various climbing methods, and because I do this, when I've "gotten into trouble," I just rappel down & start over. I just started rappelling last month, & already it will be the ONLY way that I climb a tree.
My advice- FIRST start with learning how to rappel. Decide if you want to use knots, a figure 8, or a mechanical device like a GriGri or MadRock Safeguard. There's plenty of threads with info on all of these options. Start from 1 stick & see how it goes. Then add more stix as you get comfortable with it.
I started at 3 ft up, then went to 6 ft, 9 ft, & so on. I now have a platform set at 18 ft with steps going up, & rappel from it about every other day.
Once you have that down, & are using it as your tether, you can climb a few feet off of the ground & simulate various failures- stix or steps loose, platform loose, etc. & you'll see how the tether behaves, how you swing, and become more comfortable with those situations, if they would ever occur.
I prefer Wild Edge Stepps, but also have & use Hawk Helium & Tethrd Skeletor stix. My platforms are the Tethrd Predator XL, and 2 Wild Edge Perch's
I personally have never had a platform, stick, or step fail on me.
I personally (on occasion,) have NOT attached them tight enough, & have had them slip on me a little bit- but that was MY fault, & not the device's.
I am by NO MEANS a climbing expert. But I believe that I can safely say that most mishaps are caused by CLIMBER ERROR, and that covers a wide range of things, like improper equip. use, improper knot tying, improper use of mechanical devices, general bad judgement, climber in a hurry, etc-the list goes on & on!