Does it always mean that something went wrong if you passed on an eventually successful startup? That seems like an assumption baked into the question and your answer.
At the end of the day you are taking a calculated risk. The interesting question isn't whether you wished you had funded them, because that is asking you to make a risk-free (in hindsight) decision. The real questions is how you decide whether a missed opportunity indicates a lapse in the way you calculated risk/reward, or simply a bet you ended up on the wrong side of despite it being the right bet at the time.
That's the question I'd really be interested in hearing the answer to. How do you decide whether a missed opportunity represents an error in your process?