India's Gen Z protests have shattered the aura of invincibility surrounding Prime Minister Narendra Modi. South Africa's anger has yet to find somewhere as useful to be channelled.

For 12 years, Narendra Modi has governed the world's largest democracy on a basic formula: sustained religious mobilisation wrapped in the promise of economic development and material progress. This month it met its most serious test, and one set mostly by people too young to remember India without him in charge.

For five days, tens of thousands of young Indians occupied streets in cities across the vast country, in the largest mobilisation against the prime minister thus far in his tenure. The protests have already forced Modi's government into a humiliating climbdown and claimed the scalp of a minister in his Cabinet; a concession Modi has spent a decade refusing to make to anyone.

The trigger was something as unlikely as an entry examination. In May, authorities found that the national medical school admissions test had been compromised by leaks. More than two million candidates were told to write it again, having spent years and -- in many cases -- a family's savings preparing for it. At least 12 took their own lives. A police investigation traced the leak to insiders with access to the exam process. Students demanded the resignation of Dharmendra Pradhan, the education minister, after a tenure...