Four very different mental tests, each tapping a different ability. Twelve people sat all four. Pick one test for each axis to see how those two sets of scores line up, then try another pairing, and another.
Each dot is one person. Uphill means people who score high on one test tend to score high on the other.
One honest caveat: a single factor that summarises all that overlap is real and useful, but it does not by itself prove there is one inner "engine" driving every skill. Whether g is a thing or a shadow cast by many overlapping abilities is still argued. Either way, the pattern you just traced is about as solid as findings in psychology get.
The universal positive correlation across mental tests is the positive manifold; Spearman (1904) proposed the general factor g to explain it. Illustrative data, but it behaves like real test batteries, where every pair of well-built cognitive tests intercorrelates positively.