If an engine doesn't start within 4 or 5 flips, something isn't right. Could be a bad plug, not enough glow power, failure to prime, or flooded, etc. Whatever the cause, continuing to flip over and over is pointless. If mine doesn't start within a few flips, I stop and figure out what's wrong.

But while we're on the subject of grins, I always feel sorry for people who grind a dry engine with the starter for 30 or 40 seconds because nobody ever taught them they should prime it before applying the starter.
Don't be so sure. Some people think that the prevalence of electric starters have caused people to become sloppy around the prop, leading to increased injuries once the engine is running.