How does this make sense exactly? A happy person, with more resources, would be better off not taking risks that could result in him losing what he has. On the other hand, a sad person with few resources, would need to take more risks then the happy person to get the same results.

Kaj's hypothesis is a bit off: what he's actually talking about is the explore/exploit tradeoff. An animal in a bad (but not-yet catastrophic) situation is better off exploiting available resources than scouting new ones, since in the EEA, any "bad" situation is likely to be temporary (winter, immediate presence of a predator, etc.) and it's better to ride out the situation.

OTOH, when resources are widely available, exploring is more likely to be fruitful and worthwhile.

The connection to happiness and risk-taking is more tenuous.

If you told a rich person, jump off that cliff and I'll give you a million dollars, they probably wouldn't do it. On the other hand, if you told a poor person the same thing, they might do it as long as there was a chance they could survive.

I'd be interested in seeing the results of that experiment. But "rich" and "poor" are even more loosely correlated with the variables in question - there are unhappy "rich" people and unhappy "poor" people, after all.

(In other words, this is all about internal, intuitive perceptions of resource availability, not rational assessments of actual resource availability.)