Yep they're very much based on the lottery system and you having average luck or greater. That said your investment is never at risk of going down other than subject to inflation if you have bad luck. Nothing like a 5, 10, 20% drop in the stock market at the point you wish to withdraw.Premium bonds you rarely see winnings that are bigger and consistant, unless you have over £35k in i found
Those that do win £100's and only have maybe £100 in the account or £2k, are lucky ones.
When i opened my account years ago, i was seeing the frequent £25 win when i had between £100 and £15k in, then it changed to around £50 the odd month win between £15k and £23k, then it started getting bigger wins and more frequent over £25k to 30k



