So, you are asked to sponsor something, as in a sponsored walk / run / climb / swim / whatever.
I'll bet NONE of you have ever written an amount without first checking what the people before you have put down? then weighing up everything before deciding on how much you will sponsor. Obviously if you are the first on the list, then you have to - but probably everyone after you is basing their level upon yours.
Put too little and you look stingy; put a large amount and people will say 'wow!' and make all kinds of assumptions about you from your lifestyle to the size of your car.
Checking what other people think something is worth seems to be human nature, as is feeling the pressure of being compared.
I will test it out tonight... but I know that I'll be looking at the previous amounts on the form before I sign it!