Probability of Winning Per Day Graph 100%

It depends on the current entries in a giveaway.
Often, for giveaways with a large number of copies, the graph will show a 100% chance of winning until there are more entrants. (For 5000-copy giveaways or thereabouts, it will often stay at a 100% chance, since fewer than 5000 people will enter.)

all that is needed is that you entered a single GA that has less or same number of entries as copies.

also graph is changing dynamically, so you may have entered brand new GA and was the only entry, you have 100% Win Chance, but during next 24h 1000 other people join this GA and your win chance will drop from 100% to 0,1% ;p

Being in GA groups gives you a lot better odds of winning. There's plenty of groups that you can join to create and win giveaways.

Check out the Group Recruitment Thread

Yeah, what Zelghadis said. Most likely you're the only entrant in that giveaway. So because there's one copy given away and you're the entry, currently your chances of winning that giveaway are 100%.

i just entered that giveaway so you have 0.01% less chances ^^

View attached image.