I learned a lesson today.

[gf beranek]

Ditto!

 

[theTreeSpyder]

He thought he had a knot as bight... He had a slip knot.

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A scaffold/double noose or single, maid backwards or pulled backwards on same form is a slip knot!
>>Placing Round Turn around working end rather than standing part makes slip/not noose.
Not sure that is the problem here, but that is how easy it is to have a problem!
(note in 1 move from about best shrinking eye termination to worst, where shrinks to Zer0!)
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Positive mechanical stop at end of line rules.
>>fig.8 looks more pro, has more weight , BUT same profile on stop dimension as simple overhand(fig.8 length increase doesn't increase profile where stop is needed), and simple overhand more squarely fits hole to stop, fig.8 deforms as 1 side hits stop, rest of architecture then crunches up until other side of fig.8 clogs hole

More gradual deformation of fig.8 (vs. Overhand) is very good base knot architecture, but conversely; not as stopper!
Dan Lehman is a top knot guru for IGKT, used to visit arbo boreds as knudeNoggin(knude is Danish for knot); he has tuned up my knot knowledge ruff spots more than any other anywhere! i also remeber a chat with 1 Nick from wisconsin, ohio or michigan or california (can't remember) throwing one factoid out that immediately re-aligned me square on a basic point still carried about eye made stapling or pinning thru line 2x being very strong! A benchmark model i still carry to measure other things against!
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Line is doubled overhead, but single underneath you.
Should always be able to pick up end of rope and touch chest and bight be on ground(so is now doubled over and under you), or might run out of line(some built in safety margin for rope stretch under load when descend; and your standing height on ground).
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i favored tracing line thru hand around seat, maybe even around leg, for extra friction and feel have more line as also watching.
Longer , faster descents might also have traced thru feets just rite so can pinch there for more friction etc.
Spreading out frictions is less heat build up at friction points and able to 'exhaust' easier before next friction point.
Feet together with line running thru makes first mechanical stop/braking as catcher for stopper knot.
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Making knots, rigging, should not be thought of as simply tying shoes etc. Always think like manufacturing a machine; proper alignment and form count to carry a load best, with mechanical safetys. Just because rope is so deceptively light and flexible seems different than wood and iron, but still are carefully, purposefully making machines with precisely aligned parts to task. Anything less than premium architecture is, well, LESS!