You don't really know how well you're succeeding unless you keep pushing until you don't succeed anymore. If you always succeed, then you're not pushing yourself enough.
Blech. I don't like the second person there but that sentence sounds too weird otherwise. I do try to keep pushing in many things until I fail. I've been told that it's better to go up in little increments so that I don't fail but I don't know what the increments should be until I find a breaking point. There are some situations where it's possible to determine that you're getting close to the edge. Taking a curve at speed is one. I can feel if the wheels are starting to slip and back off some. Yes, if I hit a patch of oil or ice, I'm in trouble. But that's why I practice at recovering from such things and I also try to avoid situations where I might encounter such.
There are definitely places in my life where I don't want to test until failure. My meds and work are two that come to mind immediately. But there are vast areas still to test when I remember to do so. I like feeling better.
P.S. I've edited this multiple times and thrown it away twice and while I'm not satisfied how this came out, I seem to just be changing happy to glad.