Necessity to Plan
If you can take on any problem head-on then there's little need to plan.
Brand new characters vs a thug with a club? It's probably just a fight.
Same characters vs a Giant? Planning is the only way to succeed.
The most straightforward way to do this to throw in one huge, seemingly impassible obstacle to the most obvious solution, and announce it in plenty of time to react.
- A dungeon where a force-field blocks all non-organic matter.
- A big metal monster, completely impervious to physical harm.
- You need to get past a field but it's patrolled by jerky guards riding giant birds. They'll just hover and shoot at you if you try to get through.
Opportunity to Plan
If you can't observe the bank or get hold of floorplans then it's difficult to have an exciting heist. Keep the difficulty high but give them as much information as they can take. Most importantly, for things that are really difficult, consider how much time pressure you're applying. If the only chance to rob the bank is right now then planning won't be an option. If the ideal window is in a week's time then you can really dig into the scheme.
- This terrible monster attacks every other night.
- Your assassination target recently sacked a huge number of staff. They have information and grudges.
- You have the travel diary of the last explorer to visit a distant island full of Treasure.
Ingredients for the Plan
I'm obviously biased towards interesting equipment over interesting character abilities, but both work here. If your wizard spell list is "Fireball, Magic Missile, Lightning Bolt, Sleep" then you could have an okay heist, but it's probably going to be more of a head-on assault.
If it's "Charm Person, Floating Disc, Summon Toads, Change Weather" then you're going to have to get clever, but the result will be more fun.
Likewise, if you're running Into the Odd then make sure the players have access to weird, non-obvious tools. Oddities are great here, but make sure you've got shops selling all sorts of specialist items.
- The players get a voucher worth £100, but it can only be used at an elaborate pet shop.
- A wealthy benefactor offers the complete service of his staff on your expedition, but they're mostly just house servants.
- A gifted inventor can create any electrical device you can imagine, but the more useful it is the more bulky and unreliable.