Purpose of the Lottery
The NBA Draft lottery was created to discourage teams from losing games on purpose to get better draft picks. Before the lottery existed, teams would sometimes tank, or lose intentionally, to secure the first pick. The lottery system adds an element of chance so that even teams with the worst records are not guaranteed the top pick.
How Teams Qualify
Fourteen teams qualify for the lottery: the 14 teams with the worst records during the regular season. These teams did not make the NBA Playoffs. The remaining 16 teams that made the playoffs do not participate in the lottery. Teams that made the playoffs select in order from 15th overall onward.
How the Drawing Works
During the lottery drawing, 14 ping-pong balls numbered 1 through 14 are placed in a machine. Balls are drawn one at a time to create a four-digit combination. Each of the 14 teams is assigned different number combinations based on their record and odds. When a combination is drawn, that combination's corresponding team wins that draft pick. The team with the worst record gets the most combinations and therefore the best chance at the first pick.
Odds by Team Ranking
The team with the worst record currently has a 14 percent chance of getting the first pick. The second-worst team has a 13.4 percent chance, the third-worst has 12.7 percent, and so on. The 14th-worst team has the lowest odds at around 0.5 percent. These odds mean that any of the 14 teams could potentially win the top pick, though worse teams are more likely to succeed.
What Happens After the Lottery
After the lottery determines the order of the first 14 picks, the remaining 16 teams that made the playoffs select in reverse order of their playoff seeding. The team that lost in the Finals picks 15th, and the team that won the championship picks last, at 30th overall. All 30 teams then participate in the second round of the draft. 
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