The Darien Scheme ruined the Scottish Coffers, both the royal as well as private ones.
Turns out there really isn't that much arable land or mineable resources in Panama given the technology at the time (also really dense jungle).
Those who set out mostly died in horrible ways from tropical diseases unfamiliar to the Scots who set out on their misguided mission.
While a Spanish blockade(a rather leaky one) did contribute it was complete lack of any meaningful local economic activity and diseases that really caused the downfall for the Scottish expedition to Panama.
With Scottish monied classes investing so heavily in the disastrous venture the nation was ruined financially, and was among the causes for the formal Union of Scotland and england.
Most of my info came from a wonderfully biased(but still incredibly relevant and researched) book "How the Scots Invented the Modern World" well mixed with osmosis knowledge surrounding a love of Pirates on the Spanish Main and Scottish history
In order to fully understand the motivations behind the Darien Scheme, as well as its effects, you really have to understand the state of Scotland as a nation at the end of the seventeenth century. When James VII/II was deposed much of the Scottish presbytery supported the accession of William and Mary but James was able to rally support from some of the Highland clans in the first of the Jacobite risings (this one occurring in 1689). It was, unsurprisingly, unsuccessful and James fled to France for good.
The religious motivations behind support for William and Mary, who were protestant, stem all the way back to the Restoration of Charles II and the rise of episcopacy in Scotland. Since the Reformation, the majority in Scotland had always leaned towards Presbyterianism and it was Charles I's insistence upon the establishment of an episcopacy in the 1630s that first kicked off the Wars of the Three Kingdoms (i.e., the English Civil War) when Scotland resisted the rule of bishops and thought it was worth fighting for.
In addition to the religious tensions rife in Scotland at the time were a series of bad harvests which effectively led to serious famine situations and skyrocketing prices for grain and corn. Keep in mind that the geography of Scotland is not particularly well-suited to grain cultivation in the first place so any failed harvests would make the situation even more grim. Compounding all of this was the English merchants' jealousy of trade. In order to trade anywhere after the Union of the Crowns, Scottish merchants were required to pay heavy taxes and customs on their goods because the English resented any threat to their mercantile hegemony in Britain. What they wanted was to cut the Scots out of trade altogether and therefore force the Scottish population to buy from English merchants exclusively.
Thus, Scotland figured if they could establish their own trading colonies, they wouldn't have to deal with these sorts of English sanctions and so the Darien scheme was hatched. Up until this point, the only independently Scottish colony established anywhere was Nova Scotia which was good for the provision of fish and for the basing of whaling vessels, but not so much anything else. The English East India Company, established around 1600, held a monopoly on trade to the East Indies so Scotland applied for and received a royal grant from William III for a 31-year exclusive trading right to any colonies established in South America and Asia. Originally, they hoped to gain backing from English and Dutch investors as well but were effectively cockblocked by English traders and an indifferent English government.
So, after scraping together the necessary money, ships, and venturers, they set out for Panama because the Isthmus of Panema was a strategic location and because the area that they chose had not been actively inhabited by the Spanish since around 1510. That is, although Spain had claimed Panama, the Gulf of Darien was kind of a crappy and inhospitable location and their original settlement there had been burned down by the native population and never rebuilt. So, the Scots felt that almost 200 years of non-habitation there by the Spanish made it fair game. That is, if they still wanted it, surely they would have resettled it?
Others in this thread have discussed what happened after the Scots got to Panama and what the devastating effects of the Darien failure were. Scotland was crippled so badly that she was forced to agree to the political union with England just to absolve the debts she'd incurred with this ill-fated scheme. She then effectively lost all independent trading rights which is why this whole plot was hatched in the first place. It is interesting to note though that of all the demands made by Scotland, the two that she absolutely would not compromise on were freedom of the Scottish kirk - Scotland still wanted nothing to do with bishops - and separation of the Scots legal system which remains, to this day, uniquely distinct from the common law system of England.
For further reading on this topic, I'd suggest any of the following books and articles:
Don't be put off by the fact that some of these works date from the beginning of the 20th century. I know that there's sometimes a leeriness toward using sources that are "too old" but in this case, these sources were pretty definitive and no new research has arisen to challenge the points made therein. So it's not actually that out-of-date.
Follow-up: did they go back to Scotland?
Is that a lock on the underside of the Darien Chest? Looks like modern art:
https://en.wikipedia.org/wiki/File:The_Darien_Chest,_Royal_Museum,_Edinburgh.jpg
