Now, the really critical point is this: As a pilot, you will actively be altering the chord. At the same time, though, Mother Nature might be changing the angle of attack by altering the inflow direction. And when you fly into a thermal, the inflow will be coming "from further down", which also increases the angle of attack. So, the correct reaction for a pilot would be to release the brakes to keep the angle of attack within a safe range. On the other hand, when you leave the thermal, inflow to the leading edge will be "further up", reducing the angle of attack. To keep the wing within a normal range, the pilot now needs to pull on the brakes.

So it all boils down to this: As a pilot, you are altering the chord. Meanwhile, Mother Nature is changing the inflow direction (thermals/turbulence). Together, the chord and inflow direction result in an angle of attack. When the angle is too large, the glider stalls. When it's too small, you'll get a (frontal) collapse, on one or both sides.

Luckily for us, paraglider wing design means that a stall is not possible with the brakes completely released – and that’s even when flying into very strong thermals, resulting in a large increase in the angle of attack.