I would assume it's a statement on determinism. The phrase is based on the dual usage of "just" in meaning "simply" the first time, and then "rationally" in the next. It seems the author wants you to refuse the simple understanding of things and focus on the causal chain-of-events leading up to them instead.

That's just my interpretation, though. "Just" is also commonly used as a term for religious righteousness, which could also change the meaning. I'm unfamiliar with Jim Rohn too, if that helps :P

I see the phrase as this:

- "Things don't just happen; things simply are."

- "Things don't just happen by chance; things occur for a reason."

- "There are no accidents; everything happens for a purpose."

Or, as a my teenager would say:

"Things don't just happen; things happen just because."

Thank you for all the answers.

I guess the one saying about things happening for a reason, or going further, the reason why they happen is to give us a chance to act on them in some way, talks to me the most.

See also https://en.wikipedia.org/wiki/Just-world_hypothesis

You're right to be confused, it's fairly ungrammatical, one would typically use the adjectival form there: "... things happen justly" but then it wouldn't scan as well.

It might be expressed another way as:

"Things don't merely happen; things happen as they should (as deserved/merited/earned)."