Selling a part of your business can help spread risk to a new investor reducing your own personal risk.
not getting it.
If you sell your business, it's because the value of the business to you is less than the purchase price. Likewise, the value to the buyer is greater than the purchase price.
Ideally startups are about creating value, and making a return on that value, but more and more they look like they are instead selling hype to a series of investors who are trying not to get stuck with the hot potato.
VCs have MUCH larger bankrolls and so their Kelly bet is proportionately larger, but not percentage larger.