You might have seen this video going around:
Watch it first, then I will say some things...
Ok, read on if you watched it.
I've seen some kind of overly complicated explanations of Nick's strategy, so I will give you my explanation. Nick wants to split the prize 50/50 which is understandable because that's the overall most fair outcome for both players. If his goal is to split 50/50, the one thing that will mess that up is if Abraham chooses to steal. So what Nick should do is say whatever needs to be said that would convince Abraham not to steal. This lie is actually to benefit *both* of them and ensure a fair outcome.
Nick's claim that Nick will steal leaves Abraham with the choices of a) steal (where Abraham gets nothing) or b) split (where Abraham might get 50% of the prize if Nick follows through with his promise). Abraham might choose to get nothing out of spite, but if Nick can appear genuine then he bets that a chance at 50/50 split will be more attractive that "guaranteed" getting nothing. Nick's strategy (which requires Nick to appear very confident and genuine) does deter Abraham from stealing.
If Abraham is deterred from stealing, then Nick can go ahead with splitting. Yeah Nick said he would steal, but if Nick's intention all along is to ensure a 50/50 split, there is actually no reason for him to go through with his claimed plan of stealing, then sending Abraham half the money later. Instead, now that he has "defused the bomb of the possible steal," he can simply choose split. Again, the lie was actually to benefit both players.
The only thing I'm not sure about here is why this has not been a common strategy for years. Maybe it has, though the recent popularity of this video would lead me to believe it was an unusual move.