Essentially, by buying all 1000 combinations, one will win $500 every game, but also lose $500 every game ( $1000-500=500). Person looses $1 per every $2 spent. Same goes for pairs: buy all 100 Front pairs or Back pairs and you will win $50 every game but loose $50 also every game. The game gives you the win that equals your loss. Yet to people it does not seem just. They want to win all the time. By not knowing which combinations to play to win, when people play just few tickets, their loses can be large, or they'd have occasional luck, but not constant, so losses most likely will accumulate and get larger than 50/50.
When playing pairs, it's easy to think that odds are so great, 1 to 100, they seem to be 10 times less than if playing Straight. Yet, the difference between high an low odds disappears because pay out for the win is also 10 times less, not $500, but $50.
Just divide odds by the payout: 1000:500=2. 100:50=2. That means minimal loss when playing lottery is $1 on every $2 spent. Largest loss can go exponentially.