Sometimes you get a crisis card that has a choice, such as "-1 Food OR Current Player Discards 3 Cards". In situations where you cannot afford the cost of the latter, are you forced into the former? For example, if the current player has no hand, are you required to lose 1 food?
No, in these cases you are welcome to choose the "discard 3 cards" option and merrily not do anything.
These effects of Crises are not really COSTS per se - in most games costs are non-optional, so your reasoning about being forced to do the other choice makes some sense if you think of these as costs.
But they really aren't costs, they're just the effects of that Crisis, and you're welcome to choose the one that impacts you the least, and execute as much of it as you're able to.
In the rules of the game they have a clarification which specifies this.
When a player makes a choice on a Crisis Card, he can always choose the top or bottom section of the card, regardless of whether he will be able to fulfill the game text listed (unless the card specifically restricts this)
The reason here is that this happens. Without an option, if you were forced to discard 3 cards and only had 2 it is obvious what would occur. The choice makes this issue confusing, which is why the rules have a specific clarification.
This is one of those rare "good" things for the humans.