10-15 minutes is the normal window for hand kneading, 20 at the outside - so if you're at twenty and still shaggy, the motion (or the dough) needs a look, not more suffering.
The course methods: stretch-and-combine - stretch the dough forward, fold it back, rotate, repeat with rhythm. And cross-kneading in fast 2-3 minute bursts. Both build gluten by stretching and layering it.
Slap-and-fold is completely legit, not just content - it develops gluten the same way and is especially good for wet sticky doughs that stretch-and-fold would leave glued to your palms. It just LOOKS dramatic.
Two common reasons for the never-ending knead: added fat too early (butter blocks gluten bonding, it goes in at 70-80% development), or sneaking in bench flour that keeps the dough permanently behind. Wet hands beat extra flour. And check with the windowpane at minute 12 rather than kneading to exhaustion - the dough often arrives before the arms admit it.
