I have started to feel that there must be some basic difference between the brains of people who are able to focus 100% and never falter by making silly mistakes or are able to nail comlex CR questions 2.5 hours into the test and my brain.How do i learn to focus like that?

first, you're clearly overestimating the competition here; obviously, there isn't anyone who NEVER makes "silly mistakes".

second, the issue here probably lies in finding the goal of the problem.
how often do you take the time to figure out exactly what you're looking for, before you set out looking for it?

that may sound like a stupid question, but, really, that's the issue with 99% of people who have trouble with RC and CR: they go "looking", without really having a clue what they're looking for in the first place!

for instance, take a look at #94 in the 13th edition OG CR. (I can't reproduce the problem here.)
In that problem -- before you even look at the answer choices -- you should have the following goal in mind: "I need to find something that's bad about building with bamboo ... and that pertains specifically to high land value."
THEN you go look at the choices.

if you have that kind of focus, then you should find that there really aren't any "complex" CR questions; there are just questions on which you aren't paying attention as well as you are on others.

--

really, this is just the way you think about these situations on planet earth.

for instance, the U.S. tax code is thousands and thousands of pages long.
but, if i have a "detail question" -- such as "Am I allowed to take a mileage deduction for driving from this kind of place to that kind of place?" -- then i know exactly what i'm looking for... and so it's not very hard to find.
when it comes to detail questions here, i just take the same approach that i'd take in trying to answer a tax question.

oh, and this:

I have planned to counter my silly mistakes problem and focus issue by doing 37 quant and 41 verbal questions everyday just to practice endurance.Will this practice turn on the lightbulb more often and faster?

no. in fact, that will probably have the opposite effect -- you'll just get mentally fatigued and "burn out", and then you'll make even more mistakes.

honestly, you shouldn't study CR or RC for more than, say, 10-20 lifetime hours each (and even getting toward the upper end of that range is probably excessive).
if you get past that point and are still having issues, then further "studying" isn't going to help the issue (and may even hurt you) -- you need to step back and think about GOALS. (not score goals -- goals in solving the problem.)

first, whether you even have them in the first place.
second -- if you do -- whether they're the right ones.