The point is that as the estimates get bigger, they become less likely to be accurate anyway. There's no point in debating the merits of 34 vs 35 - at that point you're likely to be miles out anyway. This way just makes it easier: does this feel more like a 20-point task or a 40-point task? Not having the numbers between 21 and 39 forces you to make look at it in this "bigger" way. It should also be a hint that you should break the task down further before you come close to doing it.
The sequence you give has been introduced by Mike Cohn in his book "Agile Estimating & Planning" (therefore the sequence is copyrighted, you need to obtain the permission to use it or you can also buy decks from his online shop).
This sequence allows you to compare backlog items to eachother. So it is imposible to say that some item is exactly two times bigger than other. Using this sequence you will always decide if it is more than two times bigger or less than two times.
For example:
First Item is estimated as 3SP
Now you are estimationg Second Item and someone said that it is two times "bigger" than First Item. Development tasks can't be exactly that same or exactle few times bigger or smaller. So you need to decide if it is bigger less than two times or more (it could be 5SP or 8SP).
Using this sequence you are putting some uncertainty into that numbers so probability that this stats will work for you become higher.
Other simple answer for your question is: Mike Cohn chose this nubers after many experiments because they seams to work best in long period of time for various teams
All what I've wrote before is theory which has been created after experiments.
I've never seen that sequence used, the Fibonacci series (1 2 3 5 8 13 21 34) is more common. The idea is to avoid tricking yourself into thinking there is precision when there isn't.
计划扑克上的数字代表任务的复杂性。例如，您不应认为价值为 8 的故事的工作量或时间是 4 号故事的两倍。您可以根据需要对这些数字使用任意多种不同的表示形式（例如 T 恤尺寸）。您只需要知道一个值比另一个值更复杂，并且还有另一个值比它更大。 Planning Poker 应用程序试图说明这一点与数字相关的绘图的复杂性，以帮助实现这个想法。
Numbers on planning poker represent complexity of a task. You should not consider that a story with 8 as value is the double size in effort or time of a size 4 story for example. You could use as many different representations for these numbers as you want (like t-shirt sizes). You just need to have an idea that one value is more complex than another and there is another value that is even more bigger than it. The Planning Poker application attempt to illustrate this complexity with drawings related with number in order to help on this idea.
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关键是，随着估计值越来越大，它们就越不可能准确。争论 34 与 35 的优劣是没有意义的——到那时你可能会相差甚远。这种方式只是让它变得更容易：这感觉更像是 20 分任务还是 40 分任务？没有 21 到 39 之间的数字迫使你以“更大”的方式来看待它。它还应该暗示您应该在接近完成任务之前进一步分解任务。
The point is that as the estimates get bigger, they become less likely to be accurate anyway. There's no point in debating the merits of 34 vs 35 - at that point you're likely to be miles out anyway. This way just makes it easier: does this feel more like a 20-point task or a 40-point task? Not having the numbers between 21 and 39 forces you to make look at it in this "bigger" way. It should also be a hint that you should break the task down further before you come close to doing it.
所有详细信息均在此处解释：http://en.wikipedia.org/wiki/Planning_poker
你给出的序列是Mike Cohn在他的书《Agile Estimating & Planning》中介绍过的（因此该序列是受版权保护的，你需要获得使用它的许可，或者你也可以从他的网上商店购买套牌）。
最初的规划扑克序列有点不同，由他的原始发明者 (James Grenning) 描述：http://renaissancesoftware.net/papers/14-papers/44-planing-poker.html
All the details are explained here: http://en.wikipedia.org/wiki/Planning_poker
The sequence you give has been introduced by Mike Cohn in his book "Agile Estimating & Planning" (therefore the sequence is copyrighted, you need to obtain the permission to use it or you can also buy decks from his online shop).
The original planning poker sequence is a bit different and described he by his original inventor (James Grenning) : http://renaissancesoftware.net/papers/14-papers/44-planing-poker.html
此顺序允许您将待办事项列表项目相互进行比较。因此，不可能说某件物品恰好是其他物品的两倍。使用这个序列，您总是可以决定它是大于两倍还是小于两倍。
例如：
第一项估计为 3SP
现在您正在估计第二项，有人说它比第一项“大”两倍。开发任务不可能完全相同，也不可能大或小几倍。因此，您需要确定它是否大于两倍或更多（可能是 5SP 或 8SP）。
如果您的待办事项中有许多估计项目，您可以使用此数字进行一些统计。这个统计数据之所以有效，是因为大数定律。 http://en.wikipedia.org/wiki/Law_of_large_numbers
使用这个序列你会带来一些不确定性进入这些数字，这样这个统计数据对你有用的可能性就会变得更高。
您的问题的其他简单答案是：Mike Cohn 经过多次实验后选择了这个数字，因为它们对于不同的团队来说在很长一段时间内效果最好
我之前写的所有内容都是已经创建的理论经过实验。
This sequence allows you to compare backlog items to eachother. So it is imposible to say that some item is exactly two times bigger than other. Using this sequence you will always decide if it is more than two times bigger or less than two times.
For example:
First Item is estimated as 3SP
Now you are estimationg Second Item and someone said that it is two times "bigger" than First Item. Development tasks can't be exactly that same or exactle few times bigger or smaller. So you need to decide if it is bigger less than two times or more (it could be 5SP or 8SP).
If you have many estimated items in your backlog you can use this numbers for some stats. This stats works because Law of large numbers. http://en.wikipedia.org/wiki/Law_of_large_numbers
Using this sequence you are putting some uncertainty into that numbers so probability that this stats will work for you become higher.
Other simple answer for your question is: Mike Cohn chose this nubers after many experiments because they seams to work best in long period of time for various teams
All what I've wrote before is theory which has been created after experiments.
我从未见过使用该序列，斐波那契数列（1 2 3 5 8 13 21 34）更常见。这样做的目的是避免欺骗自己，让自己误认为精确度并不高。
I've never seen that sequence used, the Fibonacci series (1 2 3 5 8 13 21 34) is more common. The idea is to avoid tricking yourself into thinking there is precision when there isn't.
计划扑克上的数字代表任务的复杂性。例如，您不应认为价值为 8 的故事的工作量或时间是 4 号故事的两倍。您可以根据需要对这些数字使用任意多种不同的表示形式（例如 T 恤尺寸）。您只需要知道一个值比另一个值更复杂，并且还有另一个值比它更大。 Planning Poker 应用程序试图说明这一点与数字相关的绘图的复杂性，以帮助实现这个想法。
Numbers on planning poker represent complexity of a task. You should not consider that a story with 8 as value is the double size in effort or time of a size 4 story for example. You could use as many different representations for these numbers as you want (like t-shirt sizes). You just need to have an idea that one value is more complex than another and there is another value that is even more bigger than it. The Planning Poker application attempt to illustrate this complexity with drawings related with number in order to help on this idea.