Explanation: Some leftists (not exclusively tankies, though you will always see tankies take this position) assert that Cuba's problems are due to embargoed by the US.
Despite the embargo being wrong, useless, and even counterproductive, a closer look at the situation shows that the assertion is dubious as a primary driver of Cuba's economic woes - the Soviet Union allowed Cuba to continue its role as a sugar plantation for a superpower (previously acting as such for the US) up until its fall in the 1990s - not coincidentally, Cuba's economy took a nosedive at the same time. Cuban sugar was massively subsidized by the Soviet Union as part of the clientistic relationship between the two; Castro, to his credit, invested these subsidies in public services, showing himself to be an idealist, not just a self-serving strongman. Castro, to Cuba's detriment, however, largely did not invest these subsidies into diversifying the economy.
When the Soviet Union fell, both the massive amount of material aid (such as being given machinery for free or at significantly reduced cost) and the market subsidy for sugar dried up. Cuba's strict planned economy has come back to bite it. Not only does it now lack a superpower willing to subsidize the sugar industry, but, even if the American embargo is lifted, it's doubtful that it would find the US willing to subsidy Cuban sugar to the degree that the USSR did, wherein the USSR bought Cuban sugar at six times the market price.
The embargo's biggest influences have been further straining an already-strained maintenance regime, by making relatively cheap-but-effective American machinery more expensive to acquire; and shaving a few percentage points of profit off of Cuban exports, which, considering Cuba's overall sluggish economy, is a big deal. The issue is that if Cuba's economy was not already immensely and inherently fucked, it wouldn't be such a big deal. In the 1950s, for example, Cuba was a major exporter of cattle products - in the modern day, it is a net importer which produces fewer cattle products than it did in the 1950s - a decrease not due to environmental degradation or changing economic patterns, but due to the inefficiency and Kafkaesque absurdity of hierarchical centralized planning from detached apparatchiks.
Fuck the embargo though, and fuck the racist GOP and the whinging descendants of Cuban exiles in Florida for keeping it a political football in play.