Keep on digging ou Maaikie. Just bear in mind that the closer you get to the core of the earth, the hotter it gets.
Maybe you should have a look at what exactly constitutes a bet and where the "unpredictable" part comes into play.
Bet
1. An agreement usually between two parties that the
one who has made an incorrect prediction about
an uncertain outcome will forfeit something stipulated to the other; a wager.
2. An amount or object risked in a wager; a stake.
3. One on which a stake is or can be placed:
Our team is a sure bet to win.4. a. A plan or an option considered with regard to its probable consequence:
Your best bet is to make reservations ahead of time. b. Informal A view or opinion, especially about something that cannot be known at the present time: My bet is that the rain will hold off. My bet is he didn't do it.
v. bet or
bet·ted,
bet·ting,
bets v.tr.1. To stake (an amount, for example) in a bet.
2. To make a bet with: I bet them that we would be first.
3. To make a bet on (a contestant or an outcome).
4. To maintain confidently, as if making a bet: I bet they were surprised by the news.
v.intr. To make or place a bet.
Idiom: you bet Informal Of course; surely.
Have a close look at the example given at point no 3, i.e.
Our team is a sure bet to win.