is not what people are saing, you said "rate for succes is 66% so failure is 44" this is your own logic.
and give us a break with "if you broke 2 weaopns before your chance of breaking will be 33% from 33%" cause this means like 11% . So if you enchant once more and broke the chance for failure will be 33% from 11% thats like 3%. That means you will enchant succesfully for sure. Then how do you explain my friend broke 18 weapons in a row? you know if you divide one number many times eventually he will reach something very close to 0 (this is pure math too). 33% from 33% is 11% , 33% from 11% is 3%, 33% from 3%is 1%, 33% from 1% is 0.33%, 33$ from 0.33% is 0.11% so after 18 tries how the hell he succed to broke a weapon cause after your speculation he`s rate of failure would be 0,00001.
Is alot more probably the rate of failure is 33% no mather how many times u broke before. Hell, after how many weapons I broke I should have a rate of succes now of 99%.
The single thing I can belive is this chart :
this might be possible . if you enchant a weapon the rate to succed will degrease after each enchant. Is like the enchant rate of skills.
EDIT: if you look at these numbers you will see at +4 you got 66% chance of the +3. So is allways 2/3 smaller than before.
First was 66 from 100. that means 2/3. Then 44% and 66% that means again 2/3.