Actually you are incorrect about the dice as you wouldn't have gotten just as far as when you started. While the accumulated percentage while yes, stating how lucky/unlucky you are, also directly impacts your future rolls. While the above posters are correct about it being a '50/50' chance each time, the overall chance is still increasing allowing you to with a certain number of rolls, predict with nigh on certainty what your next object fished will be.
Your interpretation is wrong. Your numbers are right. It's completely false to state that "also directly impacts your future rolls". It does in no way impact your future rolls. It only impacts how unlikely the sequence you actually got from all possible sequences is.
See accumulative probabiliy says less than people think.
Accumulative probability does not say that if 10 people do n casts and the accumulative probability being X that 10*X people will see the event. Accumulative probabilities are also subject to the law of large numbers. I.e. if your probe pool is small even if your accumulative probability says 90% should get it, testing with 10 people it is possible to see fewer than 9 people not seeing the event!
Dice or these nonprogressive random loot evens have no memory, so every cast is 1/5000. If you did 7500 loots without luck there is nothing that stored that your chance of getting it with the number of tries was 99.9%. So for the point of how likely it is for the next 7500 you have gained nothing. Past events have exactly no influence on future ones.
Let me describe this difference in another way. There are two numbers here. One describing your past bad luck and one describing your chance looking forward given that you plan to do N tries.
There is no uncertainty about the past. If you did N casts and didn't get the event with probability X, then your bad luck was 1-X. It's set, you simply did not get the event and that's it. There is no actual uncertainy involved.
For future expectations, you still have this uncertainty and an actual chance that X happens.
Now lets put the two together. You did N casts and got nothing. Your expectation looking forward to get event X is not that of 2*N attempts, because there is no probability attached to the past N events at all anymore. Your probability looking forward is again just X for the N attempts unattempted!
So paradoxically if you have done say 7500 casts and got nothing, the next 7500 cast have the same (and not more!) expectation to them as the first 7500 you did.
If this was not true, then the probability would not be constant for each event. But it is. Or in other words, probability would depend on time and/or have memory. This isn't the case.
But I wish you were right. My main critique of fishing achievements is exactly that there is no sense of progress. I have done over 11k casts for the turtle and got nothing. All I can say to that is that in the past I was insanely lucky and for the future I haven't gotten anywhere yet. For all I know I can be equally unlucky again and do another 11k without luck! Random loot is really random.
After 11k casts I do not have neigh 100% chance to get the turtle next cast. I still have a 1/5000 (or whatever the actual rate is) chance to get it. So basically what you state is just not correct. The longer I cast without a catch, the more unlucky I get. That is all. The local probability doesn't change at all. In a large pool of people some will have gotten theirs early making the statistical mean (over large number) work out to 1/5000 casts being a catch, they just not happen to be mine ;)