Others may define it more narrowly, but to me, PPC arbitrage basically involves setting up PPC ads (via Google AdWords or similar platform) and directing the traffic that results from ad clicks to a landing page or straight to an affiliate link (which many platforms don’t allow anymore).  The goal is obviously to earn more from the affiliate income than spent on the ad clicks.  You aren’t adding any value, but merely earning more from traffic than what it costs you to generate that traffic.
The other point is that it is pretty easy to get started.  You don’t need to be super rich, and you don’t need a lot of time to get started.  To say it requires no time would be a lie, but you don’t need to make anything listed above your life.  You can work at your job, invest your excess income, save to buy a rental property or rent out a room in your current house, and you start a side job online without breaking a sweat.
An obvious example is over exposure to bank stocks, which have been excellent investments for over a century.  Though a foundation of most portfolios, bank stocks do involve more risk at certain stages of the economic cycle than many realise.  Being less exposed to bank shares in the last few months could have preserved some capital.  So, a more diversified approach can help mitigate some of these risks.