Sanctions just make your enemy stronger. Even Cuba has a ton of capabilities that they wouldn't have developed without the embargo
But they're actually small enough to strangle, Russia and China sure aren't
Sanctions can also massively hamper a country's economic development. It depends on the specifics of their domestic productive capacity and natural resources. For example, Venezuela's economic hardships are primarily a result of sanctions combined with their underdeveloped domestic industry (colonial/neocolonial powers designated Venezuela a petrostate).
When a country does have capacity and resources, though, sanctions on an industry are basically the same as a protectionist tariff: they stimulate the industry domestically. Imperialists usually try to create such situations for themselves and it's great to watch them fuck up and do so on China's behalf.
Cuba is in a similar place as a sugar based economy, with fewer natural resources, and they managed to diversify to provide essential services in a way that Venezuela hasn't. Venezuela seems to just be trying to get the oil magic back. "Skill issue" as the kids say but not every place is lucky enough to get a Castro
