If you are pushing your luck, then you have been lucky already, and you are hoping to be even luckier. Having won at the roulette table, you let your augmented stack of chips ride on the same number rather than sensibly cashing them in. Having escaped from between a rock and a hard place (by the skin of your teeth!), you now decide to try your hand at navigating between Scylla and Charybdis.
This idiom is often seen in the negative imperative as the admonition Don't push your luck, which is akin, in its basic attitude toward fickle fortune, to the saying Don't tempt fate.
Note: The scholium below was written in response to a writeup (which has since disappeared) advancing the (to my mind somewhat fanciful) proposition that the English expression pushing your luck had its origin in a Uighur dicing game "known as 'Klahc' or 'Lokh'," in which players had the option of hitting ("pushing") a die in an attempt to convert a good roll into a better one.
The OED, s.v. push, mentions the expression to push one's fortune (or to push a fortune), glossing it as 'to engage actively in making one's fortune,' and quoting examples from as early as 1657.
Under the entry for luck, the OED lists not only push one's luck ('to expect or count on an even better run of good fortune than one has had already') but also synonymous expressions with crowd or ride instead of push.
In light of this cluster of semantically related idioms, it seems likely that the expression pushing your luck is native to English, rather than a calque of a Uighur gambling term.