Couldn't have said it better. It's absurd to expect precise predictions from a company that is just finding its way into the market. As you said, it's happening ALL THE TIME even among the largest companies in the world.
2016 and 2017 have been the first years since inception with substantial revenues. The collection and analysis of historical sales and marketing data is an ongoing process and will lead to more precise predictions with time. It really is just an exercise of applying some common sense.
The market seems to agree, because the share price hasn't crashed after missing guidance in 2016 and 2017.
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