"I agree with you 1,000%." I had a guy at work who would say this on a fairly regular basis. I pointed out to him several times that this was impossible. I think he understood on some level, but continues to this day to say 1,000%. I think he just likes saying it.
It was very much in style to say "give 110%" a few years ago, at least in the U.S. Although this is also theoretically impossible, as an industrial electrician, I can make this one work, and teach a valuable old man lesson at the same time. Most industrial facilities are heavily based on electric motors. Of course, the customer always wants to use the smallest motor possible that will still do the job. Unlike internal combustion engines, most electric motors are designed to run at 100% of their rated capacity continuously. This is why you can replace a 5 hp rated Briggs & Stratton small gasoline engine with a 3 hp electric motor, and whatever it is will probably work better with the "reduced" power.
However, electric motors are always rated with something called a "service factor", or "SF" on the nameplate. This is a rating which tells you whether a motor can be pushed beyond its rated capacity briefly. A typical service factor for an industrial motor is 1.2, meaning that for a short period of time, you can overload this motor by 20% without damaging it. Put another way, it can give 120% for short periods of time, e.g., on startup, when the loads are temporarily higher than they are at full running speed.
I believe that we humans have a Service Factor also. We can, in fact, give 110% (SF of 1.1) for short periods of time when necessary. However, if we are asked to give 110% on a regular basis, guess what? Just like that electric motor that is overloaded too often, we're going to burn out, and we will have to be rebuilt or replaced. Hopefully not after going down in flames.