No, that's exactly it. Those numbers will just keep on getting more precise as time goes on, though - we'll never know from the Drake equation alone, but it's the best guideline we have right now.
But, as you say, with respect to life (or at least complex multi-cellular life), we just don't know. But the Drake Equation encourages thinking like, even it's it's a 1 in a trillion chance effectively zero!, we'd have all these aliens running around. Because 1 in a trillion = 0 is pretty much what we're informed by day-to-day usage and intuition.
Avogadro's constant is 6.022 x 10^23 [1]. There are a hundred billion sets of a trillion constituent particles in ever mol of anything. A reaction that happens to water once in a trillion years would occur 20,000 times a second for each 18 mL of water.