> It's important to understand that only a small percentage of academics will ever get tenure. The rest will keep toiling away on increasingly poorly paid and desperate postdocs until they finally age out and decide to take a job in industry.

There's also a good chunk of people who fail to advance past the assistant professor level, which is pre-tenure at US institutions (not sure about other countries). And it's up or out, so if you're an assistant professor and you don't get tenure within a certain number of years, you lose your job.