What does SHOCK % actually do?

So I've tried to look up threads and wiki stuff on it, but still can't figure it out. Does Shock Chance simply lower the necessary hit damage needed to apply a shock on a target? Similar to Reduced Stun Threshold for stuns? Or is that only Shock Effect?
Or does it actually add some kind of flat % chance to shock regardless?

For example, on the Wiki it says Crits have a 100% chance to shock by default, which I assume means whenever you crit you apply a 20% damage amplification, so does that mean it doesn't matter how hard you crit, only that you do?
As in, would crits always shock, let's say Shaper, for 20% increased damage taken or do you still need a hard crit for the full effect?

increased shock effect is the damage amp. the base shock effect is calculated your damage vs targets max hp, and then increased with 'increased shock effect'

Just because you crit does NOT mean you get 20% damage amp.
The 20% shock effect comes from shocking ground or NON HIT sources of shock (crafted mod 'shock nearby enemies when you focus' type things)

This is all on the wiki page:

Increased damage from shock is capped at 50% at 10% of the target's maximum life dealt by Lightning damage, scaling down to 0% at no damage. Minimally shocking The Shaper and Uber requires a single hit of 150,000 lightning damage, while maximum shock requires a single hit of 7,400,000 lightning damage.
Increased shock effect will reduce the required damage thresholds. For example, with 100% increased Shock effect, maximum shock effect requires a hit of 5% of the target's maximum life.

This is why Beacon of Ruin is so valuable. Your shocks ALWAYS give you 15% damage amp.

Without shock chance, ONLY lightning crits will shock. This is the same for bleed, poison, chill, ignite. Without 'ailment chance', your normal hits cannot inflict the ailment.

Thanks for the feedback.
Yeah the first part about the Shock Effect I got from the wiki, that's all clear to me.

It's not quite the same with damaging ailments and Shock tho, is it? Damaging Ailments calculate the dot based on the damaging hit, they don't have a threshold they need to cross in order to apply it.

I get your comparison with Chill/Frost at least. Cold damage doesn't need a % to chill, as long as you deal enough damage I guess. But either crits or chance to freeze is needed to actually Freeze a target, so that's exactly how Shock also works, right?

So to summarize.
If I have, let's say, 100% chance to shock, but low lightning damage, I still won't shock anything?
And if I have enough lightning damage to shock even Shaper for maximum effect, but only, let's say 1% chance to shock, I will only shock him in about 1 out 100 hits?
Did I get that right?