To go one level deeper than the unpredictable weather and poor economics of the small-time farm, I think much of the "problem" of subsistence farming is cultural/societal and there's not much the rural farmers or the NGOs/charities can do to help other than one-off projects like the cassava grater that address specific, painful parts of the process, such as manual grating, but not the entire subsistence farming process/system as a whole.

We spent some time with the best and the brightest Ghanaian college students at Ashesi University [1], many of whom were middle/upper class and set on entering business and politics after graduation. Some discussed practical solutions to the problem, such as farmer co-ops. But all were fed up with the corruption and unstable governance of the country - which is actually extremely stable compared to Nigeria, Cameroon, Chad (Boko Haram). I heard that word 20 times during the half a day we spent with them - corruption this, corruption that. I left with the feeling that the current government and previous generations had let these students down, but that they were determined not to repeat those mistakes.

We also met the CEO and founder of the University, Patrick Awuah, who studied at Swarthmore in 1985 on a full scholarship and went on to work at Microsoft for 8 years as a software engineer and manager. He firmly believes in instilling ethics and self-reliance through education is the way forward for the country, and indeed the entire continent: "If you come back in 30 years, universities will be competing for the best and brightest students. I hope that universities will also be competing on things such as whose students are the most ethical. If that happens, it will change the continent."

I used to believe that religion was a crucial and effective way of passing an ethical code from one generation to the next. But every Ghanaian I met was either Christian or Muslim, and some even expressed concern for my soul when I said I wasn't religious. All taxi drivers would say a prayer and touch their jesus piece hanging from the rear view mirror before every journey (very disconcerting). I also spent some time in Afghanistan, where during the month of Ramadan, I and the other expats had to drink water out of sight in the bathroom at work when we were thirsty so as not to offend practicing muslims, and the entire country shut down after 2pm every day.

Yet despite hugely religious populations, both of these countries experience high levels of corruption, which I think isn't worse than the corruption that occurs in the US, it's just more visible - there's not enough to go around so favor currying/bribes/tribalism is more apparent than it is in wealthier nations where we've developed discrete ways of channeling and accumulating wealth. Corruption in poorer countries is very "in your face" - bribes to the police or politicians, kidnapping, torture, murder.

I'm not sure how it happened, but we were able to build better infrastructure in the US over the past 150 years - both physical (power, water, transportation, internet) and social (checks and balances, constitution, BOR, legal system, decently-managed welfare system). There was a lot of prosperity to go around, after WWII ended the great depression at least.

I suspect it had a lot to do with our financial successes following WWII and the unprecedented technological progress over the past century that allowed the majority of people in the US to prosper. I think our strong capitalist roots also helped, as we moved from an agriculture -> industrial -> services based economy (not a value judgment), while much of Africa was subjected to colonization and many of its resources, both material and human capital, were sent elsewhere. We corporatized and scaled up our agricultural sector, which has its pros (less back breaking labor, a lot more food) and cons (blander, genetically-weaker crops, danger of oligopoly). I think Mr. Awuah's comment is interesting because in 30 years, the best and the brightest Ghanaians may feel compelled to return home and improve life for their fellow Ghanaians, the same way he did after studying and working abroad.

In summary I believe more forward-thinking universities like Ashesi and more leaders like Patrick Awuah need to step forward to help instill a love for ethics, altruism, and the feeling of eating hard-earned bread after a long day of work in bright young students. This will address the core of the problem of the back-breaking labor needed for subsistence farming, but will take a long time. Until then we can chip away at edge problems, like cassava grating, and as another commenter pointed out, information access through smart phones.

This is all conjecture though, and I'm not big on either African or US history, so take my opinion with a grain of salt.

[1] In 2012, the university was ranked by PwC as the seventh most respected organisation in Ghana, becoming the first university to make the list. Ashesi's President, Dr. Patrick Awuah, was also ranked the 4th Most Respected CEO in Ghana. In 2015, Africa.com again named Ashesi among its list of top 10 African Universities (excluding South Africa). (From > https://en.wikipedia.org/wiki/Ashesi_University)