I'm not sure if I can tell you how to pass sims on CCNA exams, but I may have found a way to fail them

Here is how.
You finish a chapter and go through all excercises and follow practical labs and probably score 90%+ on practice tests, but guess what? You may not be able to put everything together and come up with a solution. For example, over the past few days, I learned everything about VLANs, but then I tested myself by trying to create a few VLANs and try to route traffic among them via a router. I failed to do so

It seemed like me pulling a truck uphill.
I believe this is one way why most poeple find sims difficult, as it doesn't tell you which chapter of the book it's gonna be about.
How can I become good at 'putting it all together'? Any ideas?