If you're stuck on a quest, mini-game or another piece of in game content try reading the walkthrough on official community-maintained wikis to make sure it's not part of the challenge of the game!
If the issue you're having isn't mentioned or described there, then it's possible that you've discovered a bug that we need to know about!
Drop Rates
For every item that can drop in-game, the rarer the item is, the less likely it is to be received.
However, unless the item has some specific rules in place, you are in no way guaranteed to receive a particular item after a certain number of attempts.
The law of averages will eventually balance everything out and whilst you could theoretically go thousands of attempts without receiving a rare drop or the specific item you're hunting for, you could also be extremely lucky and get back-to back drops!
Please bare in mind, it's not possible for us to modify these rates for individual accounts.
If you're looking for details regarding how to obtain a specific item, please refer to the above Wiki links for more information.
How to report a bug
Find out the difference between a Bug and a Technical Issue and how to submit a bug report for each version of RuneScape.