Question: Problem with a certain distribution

Hi friends! I have a problem with Random Variable. I don't understand why theoretical Mean differs from sample's Mean

restart; with(Statistics);

r := RandomVariable(NegativeBinomial(3, .1));
Mean((3-1)/(3+r-1));

0.1000000000

S := Sample(r, 10000);

d := map(unapply((3-1)/(3+t-1), t), S);

Mean(d);

0.04703520901756091

But !!

For example if p=0.2 then all is well

 

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