12 Comedians Who Died Before Their Time. by Patrick Bromley. Updated March 18, 2017. There are comics who work for decades and never produce anything of value, and then there are comics who are brilliant but die tragically before the world really has a chance to see the full extent of what they really could have done.
Your autosomal DNA is a random subset of your mother's and father's DNA (50% from each parent). Two siblings will not have the same results for the same reason that they do not look exactly the same. They do not get the exact same 50% from each parent. Even identical twins don't have exactly the same DNA (only almost exactly the same).
If I get the question right, the answer is 6.25%, not 25% as the other answer says. Its easy to calculate. Siblings share 50% of DNA on average, it also doesn't deviate much from it as the shared HIR (half identical regions) are very long and can sometimes cover the whole chromosome. There are also the least amount of recombinations within one generation. Half siblings have half of that, as the name says, so 25%.