Time decay versus a call's positive drift

A call option has a positive expected return, yet its theta (time decay) is negative. How can both be true?

Theta holds the stock price fixed, but the stock moves. By Itô, $\mathbb{E}[dC] = (\Theta + \mu S\Delta + \tfrac12\sigma^2S^2\Gamma)\,dt$. The Black-Scholes PDE gives $\Theta = rC - rS\Delta - \tfrac12\sigma^2S^2\Gamma$, so $\mathbb{E}[dC] = [rC + (\mu - r)S\Delta]\,dt > 0$: the stock's drift and the convexity gain from $\Gamma$ more than offset the decay.