Time constant.....
Now try this. Press S1 and keep it held down for all of this test. Wait for about half a minute then press S2 and hold it down until the LED has just a faint glow. The LED will not completely stop glowing because a tiny current will continue to flow through the 100k resistor.
Keep S1 down and press S2 at various time intervals. What you will find is that the capacitor needs to be allowed one hundred times longer to charge than it takes to discharge. If you press S2 more quickly than once every half minute you will find that the LED starts less brightly. This happen when the capacitor is not allowed enough time to charge.
Look at the circuit. The resistor charging the capacitor is 100 times higher resistance than the resistor that discharges the capacitor. So the capacitor discharges 100 times faster.
You have just discovered the time constant effect of a resistor and capacitor together, another very important effect that we need to be aware of when designing electronic circuits.