I figured I might have to explain this a bit further.
Okay. So right now, /u/Nigyver has 86 shards of armadyl. 100 are required for making the Armadyl Battlestaff.
Right now thoes 86 shards are worthless. They do absolutely nothing for him until he creates his battlestaff.
So he has 3 options.
Option 1 - use his 86 shards to create Dust of Armadyl.
This would give him 19,264GP/shard @ GE mid price for the dust. 1.65M for all shards into dust @ GE mid. This should be out of the question, as it's a terrible idea. That leaves us with 2 more options to pick from.
Option 2 - Never use the shards. Total profit: 0. He already has these shards. They exist regardless of what he does.
Option 3 - Get the 14 remaining shards and create the battlestaff. This clocks in at 122,260GP/shard @ GE mid so it's a hell of a lot better than making Dust and of course never using the shards ever sucks as well.
What I'm harping on with the "1M/shard" idea though is the fact that he has the 86 shards already. He could cash them out for that 1.65M and the Battlestaff is 12.2m so maybe I should say 750K/shard but I doubt the exact price I assign to these shards is the thing that's confusing you but just the general ballpark of that price.
Now, again I repeat this. He has the 86 shards. He's already gotten them, and until he uses them they are worthless. You don't want to make them into dust as that'd be a great waste of their potential value but without getting more shards or making them into dust they have no value. So, to give them the value of being part of a battlestaff you need the 14 shards to make the full 100 shards.
I think it'd be easier to understand in different terms, like a quest. If you've already done 90% of a quest, you've essentially gained nothing from it in most cases (very little, anyway) so by doing that last 10% you're getting the real reward. If you've already done the first 90% you don't need to consider it anymore. You have to ask yourself, is it worth it to get that last 10% done? Is it worth the 10% to get the rewards for what is essentially the 100%?
Similarly, he has done 86% of the staff. He only needs to consider the last 14%, he's done the 86% already. That no longer needs to be considered, and will offer him nothing (or next to nothing) if he chooses to bail out of the situation now. But if he goes through with that 14% he'll get the reward of 100%, so we need only consider if that 14% of work is worth the 100% reward.
That's horribly convoluted and incredibly poorly explained by me. I'm so sorry that I can't properly explain this, if you don't understand then please forgive me as it's my fault.