maintain contact with chassis parts as often as possible while working on, with any part of your bottom. Don't pet a cat while working on the computer and don't slide across a plush carpet.

The difference with a wrist strap is that the ground is made through a multi megohm resistance and thus the discharge current is low enough to not cause any damage or for you to feel it..

If you have a high static charge and touch the chassis you may feel the ZAP [no damage though because the current flows through the chassis to ground]. Discharge that same charge through the strap and you will feel nothing and not know that you had a charge.

I assume that you have felt ESD zaps during winter months getting into/out of cars or such. During that season I hold a key in my hand to take the arc. I hear it but don't feel it. LOL