None if the nag loses.
Almost twice as much as you can expect back if it wins.
Gambling is about taking a controlled (ie affordable) risk in the hope of disproportionate winnings.
Better to gamble on a 20 to 1 than an almost evens bet.
Meant to put "Just a bit more than your stake money back (plus your original stake) if it wins,
Not twice as much - that'd be 2 to 1.
As Tommy Cooper once quipped: "I backed a horse at 20 to 1 and it came in at a quarter past four".
Mug's game unless you gamble on really long odds where the potential returns are worth losing your nice new shirt.