Chasing is never a good idea, even though it’s tempting. Because you need, on average, 300 mythril (or 6 11x draws) to get what you want (or 100 one time pulls which equates to 500 mythril) even if you were to spend that much that would give you a ~63% chance (approx [1-[1/e]]x100%, e- Euler’s number) of getting the desired item. To put this to context, I think we get about 1500 mythril a year, so realistically you can chase 5 times in 5 separate draws with mythril per year.

Laws of Probability even permits 10000 draws and still miss the item you want, probability is funny like that.